\usepackage{import}
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+\usepackage{lmodern} % using Latin Modern to be able to use bold typewriter font
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-\usepackage{babel,textcomp,csquotes,ifimasterforside,varioref,graphicx}
+\usepackage{listings}
+\usepackage{babel,textcomp,csquotes,ifimasterforside,varioref}
+\usepackage[hidelinks]{hyperref}
+\usepackage{cleveref}
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-\usepackage{todonotes}
+\usepackage{graphicx}
+% use 'disable' before printing:
+\usepackage[]{todonotes}
+\usepackage{xspace}
+\usepackage{he-she}
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+\usepackage{multicol}
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\usepackage{perpage} %the perpage package
\MakePerPage{footnote} %the perpage package command
-\theoremstyle{plain}
+\theoremstyle{definition}
\newtheorem*{wordDef}{Definition}
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+\newcommand{\citing}[1]{~\cite{#1}}
+\newcommand{\myref}[1]{\cref{#1} on \cpageref{#1}}
+
\newcommand{\definition}[1]{\begin{wordDef}#1\end{wordDef}}
-\newcommand{\see}[1]{(see section \ref{#1})}
+\newcommand{\see}[1]{(see \myref{#1})}
+\newcommand{\See}[1]{(See \myref{#1}.)}
\newcommand{\explanation}[3]{\noindent\textbf{\textit{#1}}\\*\emph{When:}
#2\\*\emph{How:} #3\\*[-7px]}
-\newcommand{\type}[1]{\texttt{#1}}
+
+%\newcommand{\type}[1]{\lstinline{#1}}
+\newcommand{\type}[1]{\texttt{\textbf{#1}}}
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\newcommand{\methodwithref}[2]{\method{#2}\footnote{\type{#1}\method{\##2()}}}
+\newcommand{\var}[1]{\type{#1}}
+\newcommand{\refactoring}[1]{\emph{#1}}
+\newcommand{\ExtractMethod}{\refactoring{Extract Method}\xspace}
+\newcommand{\MoveMethod}{\refactoring{Move Method}\xspace}
+\newcommand{\ExtractAndMoveMethod}{\refactoring{Extract and Move Method}\xspace}
+
+\newcommand\todoin[2][]{\todo[inline, caption={2do}, #1]{
+\begin{minipage}{\textwidth-4pt}#2\end{minipage}}}
\title{Refactoring}
-\subtitle{An unfinished essay}
+\subtitle{An essay}
\author{Erlend Kristiansen}
\bibliography{bibliography/master-thesis-erlenkr-bibliography}
\chapter*{Abstract}
-Empty document.
+\todoin{\textbf{Remove all todos (including list) before delivery/printing!!!
+Can be done by removing ``draft'' from documentclass.}}
+\todoin{Write abstract}
\tableofcontents{}
\listoffigures{}
\chapter*{Preface}
-To make it clear already from the beginning: The discussions in this report must
-be seen in the context of object oriented programming languages, and Java in
-particular, since that is the language in which most of the examples will be
-given. All though the techniques discussed may be applicable to languages from
-other paradigms, they will not be the subject of this report.
+The discussions in this report must be seen in the context of object oriented
+programming languages, and Java in particular, since that is the language in
+which most of the examples will be given. All though the techniques discussed
+may be applicable to languages from other paradigms, they will not be the
+subject of this report.
\mainmatter
This question is best answered by first defining the concept of a
\emph{refactoring}, what it is to \emph{refactor}, and then discuss what aspects
-of programming that make people want to refactor their code.
+of programming make people want to refactor their code.
\section{Defining refactoring}
-Martin Fowler, in his masterpiece on refactoring \cite{refactoring}, defines a
+Martin Fowler, in his classic book on refactoring\citing{refactoring}, defines a
refactoring like this:
+
\begin{quote}
- \emph{Refactoring} (noun): a change made to the \todo{what does he mean by
- internal?} internal structure of software to make it easier to understand and
- cheaper to modify without changing its observable
- behavior.~\cite{refactoring} % page 53
+ \emph{Refactoring} (noun): a change made to the internal
+ structure\footnote{The structure observable by the programmer.} of software to
+ make it easier to understand and cheaper to modify without changing its
+ observable behavior.~\cite[p.~53]{refactoring}
\end{quote}
-This definition assign additional meaning to the word \emph{refactoring}, beyond
-the composition of the prefix \emph{re-}, usually meaning something like
-``again'' or ``anew'', and the word \emph{factoring}, that can mean to determine
-the \emph{factors} of something. Where a \emph{factor} would be close to the
-mathematical definition of something that divides a quantity, without leaving a
-remainder. Fowler is mixing the \emph{motivation} behind refactoring into his
-definition. Instead it could be made clean, only considering the mechanical and
-behavioral aspects of refactoring. That is to factor the program again, putting
-it together in a different way than before, while preserving the behavior of the
-program. An alternative definition could then be:
-
-\definition{A refactoring is a transformation
+
+\noindent This definition assigns additional meaning to the word
+\emph{refactoring}, beyond the composition of the prefix \emph{re-}, usually
+meaning something like ``again'' or ``anew'', and the word \emph{factoring},
+that can mean to isolate the \emph{factors} of something. Here a \emph{factor}
+would be close to the mathematical definition of something that divides a
+quantity, without leaving a remainder. Fowler is mixing the \emph{motivation}
+behind refactoring into his definition. Instead it could be more refined, formed
+to only consider the \emph{mechanical} and \emph{behavioral} aspects of
+refactoring. That is to factor the program again, putting it together in a
+different way than before, while preserving the behavior of the program. An
+alternative definition could then be:
+
+\definition{A \emph{refactoring} is a transformation
done to a program without altering its external behavior.}
From this we can conclude that a refactoring primarily changes how the
a refactoring.
In the extreme case one could argue that such a thing as \emph{software
-obfuscation} is to refactor. If we where to define it as a refactoring, it could
-be defined as a composite refactoring \see{intro_composite}, consisting of, for
-instance, a series of rename refactorings. (But it could of course be much more
-complex, and the mechanics of it would not exactly be carved in stone.) To
-perform some serious obfuscation one would also take advantage of techniques not
-found among established refactorings, such as removing whitespace. This might
-not even generate a different syntax tree for languages not sensitive to
-whitespace, placing it in the gray area of what kind of transformations is to be
-considered refactorings.
-
-Finally, to \emph{refactor} is (quoting Martin Fowler)
-\begin{quote}
- \ldots to restructure software by applying a series of refactorings without
- changing its observable behavior.~\cite{refactoring} % page 54, definition
-\end{quote}
+obfuscation} is refactoring. Software obfuscation is to make source code harder
+to read and analyze, while preserving its semantics. It could be done composing
+many, more or less randomly chosen, refactorings. Then the question arise
+whether it can be called a \emph{composite refactoring}
+\see{compositeRefactorings} or not? The answer is not obvious. First, there is
+no way to describe \emph{the} mechanics of software obfuscation, beacause there
+are infinitely many ways to do that. Second, \emph{obfuscation} can be thought
+of as \emph{one operation}: Either the code is obfuscated, or it is not. Third,
+it makes no sense to call software obfuscation \emph{a} refactoring, since it
+holds different meaning to different people. The last point is important, since
+one of the motivations behind defining different refactorings is to build up a
+vocabulary for software professionals to reason and discuss about programs,
+similar to the motivation behind design patterns\citing{designPatterns}. So for
+describing \emph{software obfuscation}, it might be more appropriate to define
+what you do when performing it rather than precisely defining its mechanics in
+terms of other refactorings.
\section{The etymology of 'refactoring'}
It is a little difficult to pinpoint the exact origin of the word
terminology, more than a scientific term. There is no authoritative source for a
formal definition of it.
-According to Martin Fowler~\cite{etymology-refactoring}, there may also be more
+According to Martin Fowler\citing{etymology-refactoring}, there may also be more
than one origin of the word. The most well-known source, when it comes to the
origin of \emph{refactoring}, is the Smalltalk\footnote{\emph{Smalltalk},
-object-oriented, dynamically typed, reflective programming language.}\todo{find
-reference to Smalltalk website or similar?} community and their infamous
-\emph{Refactoring
+object-oriented, dynamically typed, reflective programming language. See
+\url{http://www.smalltalk.org}} community and their infamous \emph{Refactoring
Browser}\footnote{\url{http://st-www.cs.illinois.edu/users/brant/Refactory/RefactoringBrowser.html}}
described in the article \emph{A Refactoring Tool for
-Smalltalk}~\cite{refactoringBrowser1997}, published in 1997.
-Allegedly~\cite{etymology-refactoring}, the metaphor of factoring programs was
+Smalltalk}\citing{refactoringBrowser1997}, published in 1997.
+Allegedly\citing{etymology-refactoring}, the metaphor of factoring programs was
also present in the Forth\footnote{\emph{Forth} -- stack-based, extensible
programming language, without type-checking. See \url{http://www.forth.org}}
community, and the word ``refactoring'' is mentioned in a book by Leo Brodie,
-called \emph{Thinking Forth}~\cite{brodie1984}, first published in
+called \emph{Thinking Forth}\citing{brodie1984}, first published in
1984\footnote{\emph{Thinking Forth} was first published in 1984 by the
\emph{Forth Interest Group}. Then it was reprinted in 1994 with minor
typographical corrections, before it was transcribed into an electronic edition
typeset in \LaTeX\ and published under a Creative Commons licence in 2004. The
edition cited here is the 2004 edition, but the content should essentially be as
-in 1984.}. The exact word is only printed one place\footnote{p. 232}, but the
-term \emph{factoring} is prominent in the book, that also contains a whole
-chapter dedicated to (re)factoring, and how to keep the (Forth) code clean and
-maintainable.
+in 1984.}. The exact word is only printed one place~\cite[p.~232]{brodie1984},
+but the term \emph{factoring} is prominent in the book, that also contains a
+whole chapter dedicated to (re)factoring, and how to keep the (Forth) code clean
+and maintainable.
+
\begin{quote}
\ldots good factoring technique is perhaps the most important skill for a
- Forth programmer.~\cite{brodie1984}
+ Forth programmer.~\cite[p.~172]{brodie1984}
\end{quote}
-Brodie also express what \emph{factoring} means to him:
+
+\noindent Brodie also express what \emph{factoring} means to him:
+
\begin{quote}
Factoring means organizing code into useful fragments. To make a fragment
useful, you often must separate reusable parts from non-reusable parts. The
reusable parts become new definitions. The non-reusable parts become arguments
- or parameters to the definitions.~\cite{brodie1984}
+ or parameters to the definitions.~\cite[p.~172]{brodie1984}
\end{quote}
Fowler claims that the usage of the word \emph{refactoring} did not pass between
the \emph{Forth} and \emph{Smalltalk} communities, but that it emerged
independently in each of the communities.
-\todo{more history?}
-
\section{Motivation -- Why people refactor}
-To get a grasp of what refactoring is all about, we can try to answer this
-question: \emph{Why do people refactor?} Possible answers could include: ``To
-remove duplication'' or ``to break up long methods''. Practitioners of the art
-of Design Patterns~\cite{dp} could say that they do it to introduce a
-long-needed pattern into their program's design. So it is safe to say that
-peoples' intentions are to make their programs \emph{better} in some sense. But
-what aspects of the programs are becoming improved?
+There are many reasons why people want to refactor their programs. They can for
+instance do it to remove duplication, break up long methods or to introduce
+design patterns\citing{designPatterns} into their software systems. The shared
+trait for all these are that peoples intentions are to make their programs
+\emph{better}, in some sense. But what aspects of their programs are becoming
+improved?
As already mentioned, people often refactor to get rid of duplication. Moving
-identical or similar code into methods, and maybe pushing those up or down in
+identical or similar code into methods, and maybe pushing methods up or down in
their class hierarchies. Making template methods for overlapping
-algorithms/functionality and so on. It's all about gathering what belongs
-together and putting it all in one place. And the result? The code is easier to
-maintain. When removing the implicit coupling between the code snippets, the
+algorithms/functionality and so on. It is all about gathering what belongs
+together and putting it all in one place. The resulting code is then easier to
+maintain. When removing the implicit coupling\footnote{When duplicating code,
+the code might not be coupled in other ways than that it is supposed to
+represent the same functionality. So if this functionality is going to change,
+it might need to change in more than one place, thus creating an implicit
+coupling between the multiple pieces of code.} between code snippets, the
location of a bug is limited to only one place, and new functionality need only
-to be added this one place, instead of a number of places people might not even
-remember.
-
-The same people find out that their program contains a lot of long and
-hard-to-grasp methods. Then what do they do? They begin dividing their methods
-into smaller ones, using the \emph{Extract Method}
-refactoring~\cite{refactoring}. Then they may discover something about their
-program that they weren't aware of before; revealing bugs they didn't know about
-or couldn't find due to the complex structure of their program. \todo{Proof?}
-Making the methods smaller and giving good names to the new ones clarifies the
-algorithms and enhances the \emph{understandability} of the program
-\see{magic_number_seven}. This makes simple refactoring an excellent method for
-exploring unknown program code, or code that you had forgotten that you wrote!
-
-The word \emph{simple} came up in the last section. In fact, most primitive
-refactorings are simple. The true power of them are revealed first when they are
-combined into larger --- higher level --- refactorings, called \emph{composite
-refactorings} \see{intro_composite}. Often the goal of such a series of
-refactorings is a design pattern. Thus the \emph{design} can be evolved
-throughout the lifetime of a program, opposed to designing up-front. It's all
-about being structured and taking small steps to improve a program's design.
-
-Many refactorings are aimed at lowering the coupling between different classes
-and different layers of logic. \todo{which refactorings?} Say for instance that
-the coupling between the user interface and the business logic of a program is
-lowered. Then the business logic of the program could much easier be the target
-of automated tests, increasing the productivity in the software development
-process. It is also easier to distribute (e.g. between computers) the different
-components of a program if they are sufficiently decoupled.
+to be added to this one place, instead of a number of places people might not
+even remember.
+
+A problem you often encounter when programming, is that a program contains a lot
+of long and hard-to-grasp methods. It can then help to break the methods into
+smaller ones, using the \ExtractMethod refactoring\citing{refactoring}. Then you
+may discover something about a program that you were not aware of before;
+revealing bugs you did not know about or could not find due to the complex
+structure of your program. \todo{Proof?} Making the methods smaller and giving
+good names to the new ones clarifies the algorithms and enhances the
+\emph{understandability} of the program \see{magic_number_seven}. This makes
+refactoring an excellent method for exploring unknown program code, or code that
+you had forgotten that you wrote.
+
+Most primitive refactorings are simple. Their true power is first revealed when
+they are combined into larger --- higher level --- refactorings, called
+\emph{composite refactorings} \see{compositeRefactorings}. Often the goal of
+such a series of refactorings is a design pattern. Thus the \emph{design} can be
+evolved throughout the lifetime of a program, as opposed to designing up-front.
+It is all about being structured and taking small steps to improve a program's
+design.
+
+Many software design pattern are aimed at lowering the coupling between
+different classes and different layers of logic. One of the most famous is
+perhaps the \emph{Model-View-Controller}\citing{designPatterns} pattern. It is
+aimed at lowering the coupling between the user interface and the business logic
+and data representation of a program. This also has the added benefit that the
+business logic could much easier be the target of automated tests, increasing
+the productivity in the software development process. Refactoring is an
+important tool on the way to something greater.
Another effect of refactoring is that with the increased separation of concerns
-coming out of many refactorings, the \emph{performance} is improved. When
-profiling programs, the problem parts are narrowed down to smaller parts of the
-code, which are easier to tune, and optimization can be performed only where
+coming out of many refactorings, the \emph{performance} can be improved. When
+profiling programs, the problematic parts are narrowed down to smaller parts of
+the code, which are easier to tune, and optimization can be performed only where
needed and in a more effective way.
Last, but not least, and this should probably be the best reason to refactor, is
to refactor to \emph{facilitate a program change}. If one has managed to keep
one's code clean and tidy, and the code is not bloated with design patterns that
-is not ever going to be needed, then some refactoring might be needed to
+are not ever going to be needed, then some refactoring might be needed to
introduce a design pattern that is appropriate for the change that is going to
happen.
Refactoring program code --- with a goal in mind --- can give the code itself
more value. That is in the form of robustness to bugs, understandability and
-maintainability. With the first as an obvious advantage, but with the following
-two being also very important for software development. By incorporating
-refactoring in the development process, bugs are found faster, new functionality
-is added more easily and code is easier to understand by the next person exposed
-to it, which might as well be the person who wrote it. The consequence of this,
-is that refactoring can increase the average productivity of the development
-process, and thus also add to the monetary value of a business in the long run.
-Where this last point also should open the eyes of some nearsighted managers who
-seldom see beyond the next milestone.
+maintainability. Having robust code is an obvious advantage, but
+understandability and maintainability are both very important aspects of
+software development. By incorporating refactoring in the development process,
+bugs are found faster, new functionality is added more easily and code is easier
+to understand by the next person exposed to it, which might as well be the
+person who wrote it. The consequence of this, is that refactoring can increase
+the average productivity of the development process, and thus also add to the
+monetary value of a business in the long run. The perspective on productivity
+and money should also be able to open the eyes of the many nearsighted managers
+that seldom see beyond the next milestone.
\section{The magical number seven}\label{magic_number_seven}
-\emph{The magical number seven, plus or minus two: some limits on our capacity
-for processing information}~\cite{miller1956} is an article by George A. Miller
-that was published in the journal \emph{Psychological Review} in 1956. It
+The article \emph{The magical number seven, plus or minus two: some limits on
+our capacity for processing information}\citing{miller1956} by George A.
+Miller, was published in the journal \emph{Psychological Review} in 1956. It
presents evidence that support that the capacity of the number of objects a
human being can hold in its working memory is roughly seven, plus or minus two
objects. This number varies a bit depending on the nature and complexity of the
can memorize and process a much larger amount of data than if it were to be
represented as its basic pieces. This grouping and renaming is analogous to how
many refactorings work, by grouping pieces of code and give them a new name.
-Examples are the central \emph{Extract Method} and \emph{Extract Class}
-refactorings~\cite{refactoring}.
+Examples are the fundamental \ExtractMethod and \refactoring{Extract Class}
+refactorings\citing{refactoring}.
\begin{quote}
\ldots recoding is an extremely powerful weapon for increasing the amount of
- information that we can deal with.~\cite{miller1956}
+ information that we can deal with.~\cite[p.~95]{miller1956}
\end{quote}
-An example from the article address the problem of memorizing a sequence of
+
+An example from the article addresses the problem of memorizing a sequence of
binary digits. Let us say we have the following sequence\footnote{The example
presented here is slightly modified (and shortened) from what is presented in
- the original article~\cite{miller1956}, but it is essentially the same.} of
+ the original article\citing{miller1956}, but it is essentially the same.} of
16 binary digits: ``1010001001110011''. Most of us will have a hard time
memorizing this sequence by only reading it once or twice. Imagine if we instead
translate it to this sequence: ``A273''. If you have a background from computer
Another result from the Miller article is that when the amount of information a
human must interpret increases, it is crucial that the translation from one code
to another must be almost automatic for the subject to be able to remember the
-translation, before he or she is presented with new information to recode. Thus
+translation, before \heshe is presented with new information to recode. Thus
learning and understanding how to best organize certain kinds of data is
essential to efficiently handle that kind of data in the future. This is much
-like when children learn to read. First they must learn how to recognize
-letters. Then they can learn distinct words, and later read sequences of words
-that form whole sentences. Eventually, most of them will be able to read whole
-books and briefly retell the important parts of its content. This suggest that
-the use of design patterns~\cite{dp} is a good idea when reasoning about
+like when humans learn to read. First they must learn how to recognize letters.
+Then they can learn distinct words, and later read sequences of words that form
+whole sentences. Eventually, most of them will be able to read whole books and
+briefly retell the important parts of its content. This suggest that the use of
+design patterns\citing{designPatterns} is a good idea when reasoning about
computer programs. With extensive use of design patterns when creating complex
program structures, one does not always have to read whole classes of code to
comprehend how they function, it may be sufficient to only see the name of a
\begin{quote}
Our language is tremendously useful for repackaging material into a few chunks
- rich in information.~\cite{miller1956}
+ rich in information.~\cite[p.~95]{miller1956}
\end{quote}
-Without further evidence, these results at least indicates that refactoring
+
+Without further evidence, these results at least indicate that refactoring
source code into smaller units with higher cohesion and, when needed,
introducing appropriate design patterns, should aid in the cause of creating
computer programs that are easier to maintain and has code that is easier (and
better) understood.
\section{Notable contributions to the refactoring literature}
-\todo{Update with more contributions}
+\todoin{Update with more contributions}
+
\begin{description}
\item[1992] William F. Opdyke submits his doctoral dissertation called
- \emph{Refactoring Object-Oriented Frameworks}~\cite{opdyke1992}. This
+ \emph{Refactoring Object-Oriented Frameworks}\citing{opdyke1992}. This
work defines a set of refactorings, that are behavior preserving given that
their preconditions are met. The dissertation is focused on the automation
of refactorings.
\item[1999] Martin Fowler et al.: \emph{Refactoring: Improving the Design of
- Existing Code}~\cite{refactoring}. This is maybe the most influential text
- on refactoring. It bares similarities with Opdykes thesis~\cite{opdyke1992}
+ Existing Code}\citing{refactoring}. This is maybe the most influential text
+ on refactoring. It bares similarities with Opdykes thesis\citing{opdyke1992}
in the way that it provides a catalog of refactorings. But Fowler's book is
more about the craft of refactoring, as he focuses on establishing a
vocabulary for refactoring, together with the mechanics of different
refactorings and when to perform them. His methodology is also founded on
- the principles of test-driven development.
- \item[todo] \emph{Refactoring to Patterns}\todo{include}
+ the principles of test-driven development.
+ \item[2005] Joshua Kerievsky: \emph{Refactoring to
+ Patterns}\citing{kerievsky2005}. This book is heavily influenced by Fowler's
+ \emph{Refactoring}\citing{refactoring} and the ``Gang of Four'' \emph{Design
+ Patterns}\citing{designPatterns}. It is building on the refactoring
+ catalogue from Fowler's book, but is trying to bridge the gap between
+ \emph{refactoring} and \emph{design patterns} by providing a series of
+ higher-level composite refactorings, that makes code evolve toward or away
+ from certain design patterns. The book is trying to build up the readers
+ intuition around \emph{why} one would want to use a particular design
+ pattern, and not just \emph{how}. The book is encouraging evolutionary
+ design. \See{relationToDesignPatterns}
\end{description}
-\section{Tool support}
-\todo{write, section vs. subsection}
+\section{Tool support (for Java)}\label{toolSupport}
+This section will briefly compare the refatoring support of the three IDEs
+\emph{Eclipse}\footnote{\url{http://www.eclipse.org/}}, \emph{IntelliJ
+IDEA}\footnote{The IDE under comparison is the \emph{Community Edition},
+\url{http://www.jetbrains.com/idea/}} and
+\emph{NetBeans}\footnote{\url{https://netbeans.org/}}. These are the most
+popular Java IDEs\citing{javaReport2011}.
+
+All three IDEs provide support for the most useful refactorings, like the
+different extract, move and rename refactorings. In fact, Java-targeted IDEs are
+known for their good refactoring support, so this did not appear as a big
+surprise.
+
+The IDEs seem to have excellent support for the \ExtractMethod refactoring, so
+at least they have all passed the first refactoring
+rubicon\citing{fowlerRubicon2001,secondRubicon2012}.
+
+Regarding the \MoveMethod refactoring, the \emph{Eclipse} and \emph{IntelliJ}
+IDEs do the job in very similar manners. In most situations they both do a
+satisfying job by producing the expected outcome. But they do nothing to check
+that the result does not break the semantics of the program \see{correctness}.
+The \emph{NetBeans} IDE implements this refactoring in a somewhat
+unsophisticated way. For starters, its default destination for the move is
+itself, although it refuses to perform the refactoring if chosen. But the worst
+part is, that if moving the method \method{f} of the class \type{C} to the class
+\type{X}, it will break the code. The result is shown in
+\myref{lst:moveMethod_NetBeans}.
+
+\begin{listing}
+\begin{multicols}{2}
+\begin{minted}[samepage]{java}
+public class C {
+ private X x;
+ ...
+ public void f() {
+ x.m();
+ x.n();
+ }
+}
+\end{minted}
+
+\columnbreak
+
+\begin{minted}[samepage]{java}
+public class X {
+ ...
+ public void f(C c) {
+ c.x.m();
+ c.x.n();
+ }
+}
+\end{minted}
+\end{multicols}
+\caption{Moving method \method{f} from \type{C} to \type{X}.}
+\label{lst:moveMethod_NetBeans}
+\end{listing}
+
+NetBeans will try to make code that call the methods \method{m} and \method{n}
+of \type{X} by accessing them through \var{c.x}, where \var{c} is a parameter of
+type \type{C} that is added the method \method{f} when it is moved. (This is
+seldom the desired outcome of this refactoring, but ironically, this ``feature''
+keeps NetBeans from breaking the code in the example from \myref{correctness}.)
+If \var{c.x} for some reason is inaccessible to \type{X}, as in this case, the
+refactoring breaks the code, and it will not compile. NetBeans presents a
+preview of the refactoring outcome, but the preview does not catch it if the IDE
+is about break the program.
+
+The IDEs under investigation seems to have fairly good support for primitive
+refactorings, but what about more complex ones, such as the \refactoring{Extract
+Class}\citing{refactoring}? The \refactoring{Extract Class} refactoring works by
+creating a class, for then to move members to that class and access them from
+the old class via a reference to the new class. \emph{IntelliJ} handles this in
+a fairly good manner, although, in the case of private methods, it leaves unused
+methods behind. These are methods that delegate to a field with the type of the
+new class, but are not used anywhere. \emph{Eclipse} has added (or withdrawn)
+its own quirk to the Extract Class refactoring, and only allows for
+\emph{fields} to be moved to a new class, \emph{not methods}. This makes it
+effectively only extracting a data structure, and calling it
+\refactoring{Extract Class} is a little misleading. One would often be better
+off with textual extract and paste than using the Extract Class refactoring in
+Eclipse. When it comes to \emph{NetBeans}, it does not even seem to have made an
+attempt on providing this refactoring. (Well, it probably has, but it does not
+show in the IDE.)
+
+\todoin{Visual Studio (C++/C\#), Smalltalk refactoring browser?,
+second refactoring rubicon?}
+
+\section{The relation to design patterns}\label{relationToDesignPatterns}
+
+\emph{Refactoring} and \emph{design patterns} have at least one thing in common,
+they are both promoted by advocates of \emph{clean code}\citing{cleanCode} as
+fundamental tools on the road to more maintanable and extendable source code.
+
+\begin{quote}
+ Design patterns help you determine how to reorganize a design, and they can
+ reduce the amount of refactoring you need to do
+ later.~\cite[p.~353]{designPatterns}
+\end{quote}
+
+Although sometimes associated with
+over-engineering\citing{kerievsky2005,refactoring}, design patterns are in
+general assumed to be good for maintainability of source code. That may be
+because many of them are designed to support the \emph{open/closed principle} of
+object-oriented programming. The principle was first formulated by Bertrand
+Meyer, the creator of the Eiffel programming language, like this: ``Modules
+should be both open and closed.''\citing{meyer1988} It has been popularized,
+with this as a common version:
+
+\begin{quote}
+ Software entities (classes, modules, functions, etc.) should be open for
+ extension, but closed for modification.\footnote{See
+ \url{http://c2.com/cgi/wiki?OpenClosedPrinciple} or
+ \url{https://en.wikipedia.org/wiki/Open/closed_principle}}
+\end{quote}
+
+Maintainability is often thought of as the ability to be able to introduce new
+functionality without having to change too much of the old code. When
+refactoring, the motivation is often to facilitate adding new functionality. It
+is about factoring the old code in a way that makes the new functionality being
+able to benefit from the functionality already residing in a software system,
+without having to copy old code into new. Then, next time someone shall add new
+functionality, it is less likely that the old code has to change. Assuming that
+a design pattern is the best way to get rid of duplication and assist in
+implementing new functionality, it is reasonable to conclude that a design
+pattern often is the target of a series of refactorings. Having a repertoire of
+design patterns can also help in knowing when and how to refactor a program to
+make it reflect certain desired characteristics.
+
+\begin{quote}
+ There is a natural relation between patterns and refactorings. Patterns are
+ where you want to be; refactorings are ways to get there from somewhere
+ else.~\cite[p.~107]{refactoring}
+\end{quote}
+
+This quote is wise in many contexts, but it is not always appropriate to say
+``Patterns are where you want to be\ldots''. \emph{Sometimes}, patterns are
+where you want to be, but only because it will benefit your design. It is not
+true that one should always try to incorporate as many design patterns as
+possible into a program. It is not like they have intrinsic value. They only add
+value to a system when they support its design. Otherwise, the use of design
+patterns may only lead to a program that is more complex than necessary.
+
+\begin{quote}
+ The overuse of patterns tends to result from being patterns happy. We are
+ \emph{patterns happy} when we become so enamored of patterns that we simply
+ must use them in our code.~\cite[p.~24]{kerievsky2005}
+\end{quote}
+
+This can easily happen when relying largely on up-front design. Then it is
+natural, in the very beginning, to try to build in all the flexibility that one
+believes will be necessary throughout the lifetime of a software system.
+According to Joshua Kerievsky ``That sounds reasonable --- if you happen to be
+psychic.''~\cite[p.~1]{kerievsky2005} He is advocating what he believes is a
+better approach: To let software continually evolve. To start with a simple
+design that meets today's needs, and tackle future needs by refactoring to
+satisfy them. He believes that this is a more economic approach than investing
+time and money into a design that inevitably is going to change. By relying on
+continuously refactoring a system, its design can be made simpler without
+sacrificing flexibility. To be able to fully rely on this approach, it is of
+utter importance to have a reliable suit of tests to lean on. \See{testing} This
+makes the design process more natural and less characterized by difficult
+decisions that has to be made before proceeding in the process, and that is
+going to define a project for all of its unforeseeable future.
-\section{Relation to design patterns}
-\todo{write, section vs. subsection, refactoring to patterns?}
\begin{comment}
\section{Classification of refactorings}
\section{The impact on software quality}
-\subsection{What is meant by quality?}
+\subsection{What is software quality?}
The term \emph{software quality} has many meanings. It all depends on the
context we put it in. If we look at it with the eyes of a software developer, it
-usually mean that the software is easily maintainable and testable, or in other
+usually means that the software is easily maintainable and testable, or in other
words, that it is \emph{well designed}. This often correlates with the
management scale, where \emph{keeping the schedule} and \emph{customer
satisfaction} is at the center. From the customers point of view, in addition to
\subsection{The impact on performance}
\begin{quote}
- Refactoring certainly will make software go more slowly, but it also makes the
- software more amenable to performance tuning.~\cite{refactoring} % page 69
+ Refactoring certainly will make software go more slowly\footnote{With todays
+ compiler optimization techniques and performance tuning of e.g. the Java
+virtual machine, the penalties of object creation and method calls are
+debatable.}, but it also makes the software more amenable to performance
+tuning.~\cite[p.~69]{refactoring}
\end{quote}
-There is a common belief that refactoring compromises performance, due to
-increased degree of indirection and that polymorphism is slower than
+
+\noindent There is a common belief that refactoring compromises performance, due
+to increased degree of indirection and that polymorphism is slower than
conditionals.
-In a survey, Demeyer~\cite{demeyer2002} disproves this view in the case of
-polymorphism. He is doing an experiment on, what he calls, ``Transform Self Type
+In a survey, Demeyer\citing{demeyer2002} disproves this view in the case of
+polymorphism. He did an experiment on, what he calls, ``Transform Self Type
Checks'' where you introduce a new polymorphic method and a new class hierarchy
to get rid of a class' type checking of a ``type attribute``. He uses this kind
of transformation to represent other ways of replacing conditionals with
polymorphism as well. The experiment is performed on the C++ programming
-language and with three different compilers and platforms. \todo{But is the
-result better?} Demeyer concludes that, with compiler optimization turned on,
-polymorphism beats middle to large sized if-statements and does as well as
-case-statements. (In accordance with his hypothesis, due to similarities
-between the way C++ handles polymorphism and case-statements.)
+language and with three different compilers and platforms. Demeyer concludes
+that, with compiler optimization turned on, polymorphism beats middle to large
+sized if-statements and does as well as case-statements. (In accordance with
+his hypothesis, due to similarities between the way C++ handles polymorphism and
+case-statements.)
+
\begin{quote}
The interesting thing about performance is that if you analyze most programs,
- you find that they waste most of their time in a small fraction of the code.
- ~\cite{refactoring}
+ you find that they waste most of their time in a small fraction of the
+ code.~\cite[p.~70]{refactoring}
\end{quote}
-So, although an increased amount of method calls could potentially slow down
-programs, one should avoid premature optimization and sacrificing good design,
-leaving the performance tuning until after profiling\footnote{For and example of
- a Java profiler, check out VisualVM: \url{http://visualvm.java.net/}} the
- software and having isolated the actual problem areas.
-
+\noindent So, although an increased amount of method calls could potentially
+slow down programs, one should avoid premature optimization and sacrificing good
+design, leaving the performance tuning until after profiling\footnote{For and
+ example of a Java profiler, check out VisualVM:
+ \url{http://visualvm.java.net/}} the software and having isolated the actual
+ problem areas.
-\section{Composite refactorings} \label{intro_composite}
+\section{Composite refactorings}\label{compositeRefactorings}
\todo{motivation, examples, manual vs automated?, what about refactoring in a
very large code base?}
Generally, when thinking about refactoring, at the mechanical level, there are
essentially two kinds of refactorings. There are the \emph{primitive}
-refactorings, and the \emph{composite} refactorings. A primitive refactoring can
-be defined like this:
-
-\definition{A primitive refactoring is a refactoring that cannot be expressed in
-terms of other refactorings.}
-
-Examples are the \emph{Pull Up Field} and \emph{Pull Up Method}
-refactorings~\cite{refactoring}, that moves members up in their class
-hierarchies. A composite refactoring is more complex, and can be defined like
-this:
-
-\definition{A composite refactoring is a refactoring that can be expressed in
-terms of two or more primitive refactorings.}
-
-An example of a composite refactoring is the \emph{Extract Superclass}
-refactoring~\cite{refactoring}. In its simplest form, it is composed of the
-previously described primitive refactorings, in addition to the \emph{Pull Up
-Constructor Body} refactoring~\cite{refactoring}. It works by creating an
-abstract superclass that the target class(es) inherits from, then by applying
-\emph{Pull Up Field}, \emph{Pull Up Method} and \emph{Pull Up Constructor Body}
-on the members that are to be members of the new superclass. For an overview of
-the \emph{Extract Superclass} refactoring, see figure
-\ref{fig:extractSuperclass}.
+refactorings, and the \emph{composite} refactorings.
+
+\definition{A \emph{primitive refactoring} is a refactoring that cannot be
+expressed in terms of other refactorings.}
+
+\noindent Examples are the \refactoring{Pull Up Field} and \refactoring{Pull Up
+Method} refactorings\citing{refactoring}, that move members up in their class
+hierarchies.
+
+\definition{A \emph{composite refactoring} is a refactoring that can be
+expressed in terms of two or more other refactorings.}
+
+\noindent An example of a composite refactoring is the \refactoring{Extract
+Superclass} refactoring\citing{refactoring}. In its simplest form, it is composed
+of the previously described primitive refactorings, in addition to the
+\refactoring{Pull Up Constructor Body} refactoring\citing{refactoring}. It works
+by creating an abstract superclass that the target class(es) inherits from, then
+by applying \refactoring{Pull Up Field}, \refactoring{Pull Up Method} and
+\refactoring{Pull Up Constructor Body} on the members that are to be members of
+the new superclass. For an overview of the \refactoring{Extract Superclass}
+refactoring, see \myref{fig:extractSuperclass}.
\begin{figure}[h]
\centering
- \includegraphics[angle=270,width=\linewidth]{extractSuperclass.pdf}
+ \includegraphics[angle=270,width=\linewidth]{extractSuperclassItalic.pdf}
\caption{The Extract Superclass refactoring}
\label{fig:extractSuperclass}
\end{figure}
\section{Manual vs. automated refactorings}
-Refactoring is something every programmer does, even if he or she does not known
+Refactoring is something every programmer does, even if \heshe does not known
the term \emph{refactoring}. Every refinement of source code that does not alter
the program's behavior is a refactoring. For small refactorings, such as
-\emph{Extract Method}, executing it manually is a manageable task, but is still
-prone to errors. Getting it right the first time is not easy, considering the
+\ExtractMethod, executing it manually is a manageable task, but is still prone
+to errors. Getting it right the first time is not easy, considering the method
signature and all the other aspects of the refactoring that has to be in place.
Take for instance the renaming of classes, methods and fields. For complex
programs these refactorings are almost impossible to get right. Attacking them
with textual search and replace, or even regular expressions, will fall short on
these tasks. Then it is crucial to have proper tool support that can perform
-them automatically. Tools that can parse source code and thus has semantic
-knowledge about which occurrences of which names that belongs to what construct
-in the program. For even trying to perform one of these complex task manually,
-one would have to be very confident on the existing test suite \see{tdd}.
+them automatically. Tools that can parse source code and thus have semantic
+knowledge about which occurrences of which names belong to what construct in the
+program. For even trying to perform one of these complex task manually, one
+would have to be very confident on the existing test suite \see{testing}.
-\section{Correctness of refactorings}
-\todo{Volker's example?}
+\section{Correctness of refactorings}\label{correctness}
For automated refactorings to be truly useful, they must show a high degree of
-behavior preservation. This might seem obvious, but there are examples of
-refactorings in existing tools that break programs. This is one of them:
-
-\begin{listing}
-\begin{minted}[linenos]{java}
+behavior preservation. This last sentence might seem obvious, but there are
+examples of refactorings in existing tools that break programs. I will now
+present an example of an \ExtractMethod refactoring followed by a \MoveMethod
+refactoring that breaks a program in both the \emph{Eclipse} and \emph{IntelliJ}
+IDEs\footnote{The NetBeans IDE handles this particular situation without
+ altering ther program's beavior, mainly because its Move Method refactoring
+ implementation is a bit rancid in other ways \see{toolSupport}.}. The
+ following piece of code shows the target for the composed refactoring:
+
+\begin{minted}[linenos,samepage]{java}
public class C {
public X x = new X();
-
+
public void f() {
x.m(this);
x.n();
}
}
\end{minted}
-\caption{A Java Program}
-\end{listing}
-\section{Test Driven Development}\label{tdd}
+\noindent The next piece of code shows the destination of the refactoring. Note
+that the method \method{m(C c)} of class \type{C} assigns to the field \var{x}
+of the argument \var{c} that has type \type{C}:
+
+\begin{minted}[samepage]{java}
+public class X {
+ public void m(C c) {
+ c.x = new X();
+ }
+ public void n() {}
+}
+\end{minted}
+
+The refactoring sequence works by extracting line 5 and 6 from the original
+class \type{C} into a method \method{f} with the statements from those lines as
+its method body. The method is then moved to the class \type{X}. The result is
+shown in the following two pieces of code:
+
+\begin{minted}[linenos,samepage]{java}
+public class C {
+ public X x = new X();
+
+ public void f() {
+ x.f(this);
+ }
+}
+\end{minted}
+
+\begin{minted}[linenos,samepage]{java}
+public class X {
+ public void m(C c) {
+ c.x = new X();
+ }
+ public void n() {}
+ public void f(C c) {
+ m(c);
+ n();
+ }
+}
+\end{minted}
+
+After the refactoring, the method \method{f} of class \type{C} is calling the
+method \method{f} of class \type{X}, and the program now behaves different than
+before. (See line 5 of the version of class \type{C} after the refactoring.)
+Before the refactoring, the methods \method{m} and \method{n} of class \type{X}
+are called on different object instances (see line 5 and 6 of the original class
+\type{C}). After, they are called on the same object, and the statement on line
+3 of class \type{X} (the version after the refactoring) no longer have any
+ effect in our example.
+
+The bug introduced in the previous example is of such a nature\footnote{Caused
+ by aliasing. See \url{https://en.wikipedia.org/wiki/Aliasing_(computing)}}
+ that it is very difficult to spot if the refactored code is not covered by
+ tests. It does not generate compilation errors, and will thus only result in
+ a runtime error or corrupted data, which might be hard to detect.
+
+\section{Refactoring and the importance of testing}\label{testing}
+\begin{quote}
+ If you want to refactor, the essential precondition is having solid
+ tests.\citing{refactoring}
+\end{quote}
+
+When refactoring, there are roughly three classes of errors that can be made.
+The first class of errors are the ones that make the code unable to compile.
+These \emph{compile-time} errors are of the nicer kind. They flash up at the
+moment they are made (at least when using an IDE), and are usually easy to fix.
+The second class are the \emph{runtime} errors. Although they take a bit longer
+to surface, they usually manifest after some time in an illegal argument
+exception, null pointer exception or similar during the program execution.
+These kind of errors are a bit harder to handle, but at least they will show,
+eventually. Then there are the \emph{behavior-changing} errors. These errors are
+of the worst kind. They do not show up during compilation and they do not turn
+on a blinking red light during runtime either. The program can seem to work
+perfectly fine with them in play, but the business logic can be damaged in ways
+that will only show up over time.
+
+For discovering runtime errors and behavior changes when refactoring, it is
+essential to have good test coverage. Testing in this context means writing
+automated tests. Manual testing may have its uses, but when refactoring, it is
+automated unit testing that dominate. For discovering behavior changes it is
+especially important to have tests that cover potential problems, since these
+kind of errors does not reveal themselves.
+
+Unit testing is not a way to \emph{prove} that a program is correct, but it is a
+way to make you confindent that it \emph{probably} works as desired. In the
+context of test driven development (commonly known as TDD), the tests are even a
+way to define how the program is \emph{supposed} to work. It is then, by
+definition, working if the tests are passing.
+
+If the test coverage for a code base is perfect, then it should, theoretically,
+be risk-free to perform refactorings on it. This is why automated tests and
+refactoring are such a great match.
+
+\subsection{Testing the code from correctness section}
+The worst thing that can happen when refactoring is to introduce changes to the
+behavior of a program, as in the example on \myref{correctness}. This example
+may be trivial, but the essence is clear. The only problem with the example is
+that it is not clear how to create automated tests for it, without changing it
+in intrusive ways.
+
+Unit tests, as they are known from the different xUnit frameworks around, are
+only suitable to test the \emph{result} of isolated operations. They can not
+easily (if at all) observe the \emph{history} of a program.
+
+
+\todoin{Write \ldots}
+
+Assuming a sequential (non-concurrent) program:
+
+\begin{minted}{java}
+tracematch (C c, X x) {
+ sym m before:
+ call(* X.m(C)) && args(c) && cflow(within(C));
+ sym n before:
+ call(* X.n()) && target(x) && cflow(within(C));
+ sym setCx after:
+ set(C.x) && target(c) && !cflow(m);
+
+ m n
+
+ { assert x == c.x; }
+}
+\end{minted}
+
+%\begin{minted}{java}
+%tracematch (X x1, X x2) {
+% sym m before:
+% call(* X.m(C)) && target(x1);
+% sym n before:
+% call(* X.n()) && target(x2);
+% sym setX after:
+% set(C.x) && !cflow(m) && !cflow(n);
+%
+% m n
+%
+% { assert x1 != x2; }
+%}
+%\end{minted}
+
+\section{The project}
+The aim of this project will be to investigate the relationship between a
+composite refactoring composed of the \ExtractMethod and \MoveMethod
+refactorings, and its impact on one or more software metrics.
+
+The composition of \ExtractMethod and \MoveMethod springs naturally out of the
+need to move procedures closer to the data they manipulate. This composed
+refactoring is not well described in the literature, but it is implemented in at
+least one tool called
+\emph{CodeRush}\footnote{\url{https://help.devexpress.com/\#CodeRush/CustomDocument3519}},
+that is an extension for \emph{MS Visual
+Studio}\footnote{\url{http://www.visualstudio.com/}}. In CodeRush it is called
+\emph{Extract Method to
+Type}\footnote{\url{https://help.devexpress.com/\#CodeRush/CustomDocument6710}},
+but I choose to call it \ExtractAndMoveMethod, since I feel it better
+communicates which primitive refactorings it is composed of.
+
+For the metrics, I will at least measure the \emph{Coupling between object
+classes} (CBO) metric that is described by Chidamber and Kemerer in their
+article \emph{A Metrics Suite for Object Oriented
+Design}\citing{metricsSuite1994}.
+
+The project will then consist in implementing the \ExtractAndMoveMethod
+refactoring, as well as executing it over a larger code base. Then the effect of
+the change must be measured by calculating the chosen software metrics both
+before and after the execution. To be able to execute the refactoring
+automatically I have to make it analyze code to determine the best selections to
+extract into new methods.
\section{Software metrics}
+\todoin{Is this the appropriate place to have this section?}
%\part{The project}
%\chapter{Planning the project}
\chapter{\ldots}
-\todo{write}
+\todoin{write}
\section{The problem statement}
\section{Choosing the target language}
Choosing which programming language to use as the target for manipulation is not
-a very difficult task. The language have to be an object-oriented programming
+a very difficult task. The language has to be an object-oriented programming
language, and it must have existing tool support for refactoring. The
\emph{Java} programming language\footnote{\url{https://www.java.com/}} is the
dominating language when it comes to examples in the literature of refactoring,
program, and the most popular IDEs that support Java, generally have quite good
refactoring support.
-The main contenders for this thesis is the \emph{Eclipse
-IDE}\footnote{\url{http://www.eclipse.org/}}, with the \emph{Java development
-tools} (JDT), the \emph{IntelliJ IDEA Community
-Edition}\footnote{\url{http://www.jetbrains.com/idea/}} and the \emph{NetBeans
-IDE}\footnote{\url{https://netbeans.org/}}. Eclipse and NetBeans are both free,
-open source and community driven, while the IntelliJ IDEA has an open sourced
-community edition that is free of charge, but also offer an \emph{Ultimate
-Edition} with an extended set of features, at additional cost. All three IDEs
-supports adding plugins to extend their functionality and tools that can be used
-to parse and analyze Java source code. \todo{investigate if this is true} But
-one of the IDEs stand out as a favorite, and that is the \emph{Eclipse IDE}.
-This is the most popular~\cite{javaReport2011} among them and seems to be de
-facto standard IDE for Java development regardless of platform.
+The main contenders for this thesis is the \emph{Eclipse IDE}, with the
+\emph{Java development tools} (JDT), the \emph{IntelliJ IDEA Community Edition}
+and the \emph{NetBeans IDE}. \See{toolSupport} Eclipse and NetBeans are both
+free, open source and community driven, while the IntelliJ IDEA has an open
+sourced community edition that is free of charge, but also offer an
+\emph{Ultimate Edition} with an extended set of features, at additional cost.
+All three IDEs supports adding plugins to extend their functionality and tools
+that can be used to parse and analyze Java source code. But one of the IDEs
+stand out as a favorite, and that is the \emph{Eclipse IDE}. This is the most
+popular\citing{javaReport2011} among them and seems to be de facto standard IDE
+for Java development regardless of platform.
+
\chapter{Refactorings in Eclipse JDT: Design, Shortcomings and Wishful
Thinking}\label{ch:jdt_refactorings}
the refactoring in a single step. This is not the way it appears when a sequence
of JDT refactorings is executed. It leaves the undo history filled up with
individual undo actions corresponding to every single JDT refactoring in the
-sequence. This problem is not trivial to handle in Eclipse. (See section
-\ref{hacking_undo_history}.)
+sequence. This problem is not trivial to handle in Eclipse.
+\See{hacking_undo_history}
\section{Wishful Thinking}
-
-
+\todoin{???}
\chapter{Composite Refactorings in Eclipse}
\section{A Simple Ad Hoc Model}
-As pointed out in chapter \ref{ch:jdt_refactorings}, the Eclipse JDT refactoring
-model is not very well suited for making composite refactorings. Therefore a
-simple model using changer objects (of type \type{RefaktorChanger}) is used as
-an abstraction layer on top of the existing Eclipse refactorings.
+As pointed out in \myref{ch:jdt_refactorings}, the Eclipse JDT refactoring model
+is not very well suited for making composite refactorings. Therefore a simple
+model using changer objects (of type \type{RefaktorChanger}) is used as an
+abstraction layer on top of the existing Eclipse refactorings, instead of
+extending the \typewithref{org.eclipse.ltk.core.refactoring}{Refactoring} class.
+
+The use of an additional abstraction layer is a deliberate choice. It is due to
+the problem of creating a composite
+\typewithref{org.eclipse.ltk.core.refactoring}{Change} that can handle text
+changes that interfere with each other. Thus, a \type{RefaktorChanger} may, or
+may not, take advantage of one or more existing refactorings, but it is always
+intended to make a change to the workspace.
+
+\subsection{A typical \type{RefaktorChanger}}
+The typical refaktor changer class has two responsibilities, checking
+preconditions and executing the requested changes. This is not too different
+from the responsibilities of an LTK refactoring, with the distinction that a
+refaktor changer also executes the change, while an LTK refactoring is only
+responsible for creating the object that can later be used to do the job.
+
+Checking of preconditions is typically done by an
+\typewithref{no.uio.ifi.refaktor.analyze.analyzers}{Analyzer}. If the
+preconditions validate, the upcoming changes are executed by an
+\typewithref{no.uio.ifi.refaktor.change.executors}{Executor}.
\section{The Extract and Move Method Refactoring}
%The Extract and Move Method Refactoring is implemented mainly using these
\subsection{The Building Blocks}
This is a composite refactoring, and hence is built up using several primitive
-refactorings. These basic building blocks are, as its name implies, the Extract
-Method Refactoring \cite{refactoring} and the Move Method Refactoring
-\cite{refactoring}. In Eclipse, the implementations of these refactorings are
-found in the classes
+refactorings. These basic building blocks are, as its name implies, the
+\ExtractMethod refactoring\citing{refactoring} and the \MoveMethod
+refactoring\citing{refactoring}. In Eclipse, the implementations of these
+refactorings are found in the classes
\typewithref{org.eclipse.jdt.internal.corext.refactoring.code}{ExtractMethodRefactoring}
and
\typewithref{org.eclipse.jdt.internal.corext.refactoring.structure}{MoveInstanceMethodProcessor},
unit\typeref{org.eclipse.jdt.core.ICompilationUnit}, the offset into the source
code where the extraction shall start, and the length of the source to be
extracted. Then you have to set the method name for the new method together with
-which access modifier that shall be used and some not so interesting parameters.
+its visibility and some not so interesting parameters.
\subsubsection{The MoveInstanceMethodProcessor Class}
-For the Move Method the processor requires a little more advanced input than
+For the Move Method, the processor requires a little more advanced input than
the class for the Extract Method. For construction it requires a method
-handle\typeref{org.eclipse.jdt.core.IMethod} from the Java Model for the method
-that is to be moved. Then the target for the move have to be supplied as the
-variable binding from a chosen variable declaration. In addition to this, one
-have to set some parameters regarding setters/getters and delegation.
+handle\typeref{org.eclipse.jdt.core.IMethod} for the method that is to be moved.
+Then the target for the move have to be supplied as the variable binding from a
+chosen variable declaration. In addition to this, one have to set some
+parameters regarding setters/getters, as well as delegation.
-To make a whole refactoring from the processor, one have to construct a
-\type{MoveRefactoring} from it.
+To make a working refactoring from the processor, one have to create a
+\type{MoveRefactoring} with it.
\subsection{The ExtractAndMoveMethodChanger Class}
+
The \typewithref{no.uio.ifi.refaktor.changers}{ExtractAndMoveMethodChanger}
-class, that is a subclass of the class
-\typewithref{no.uio.ifi.refaktor.changers}{RefaktorChanger}, is the class
-responsible for composing the \type{ExtractMethodRefactoring} and the
-\type{MoveRefactoring}. Its constructor takes a project
-handle\typeref{org.eclipse.core.resources.IProject}, the method name for the new
-method and a \typewithref{no.uio.ifi.refaktor.utils}{SmartTextSelection}.
-
-A \type{SmartTextSelection} is basically a text
-selection\typeref{org.eclipse.jface.text.ITextSelection} object that enforces
-the providing of the underlying document during creation. I.e. its
-\methodwithref{no.uio.ifi.refaktor.utils.SmartTextSelection}{getDocument} method
-will never return \type{null}.
-
-Before extracting the new method, the possible targets for the move operation is
-found with the help of an
-\typewithref{no.uio.ifi.refaktor.extractors}{ExtractAndMoveMethodPrefixesExtractor}.
-The possible targets is computed from the prefixes that the extractor returns
-from its
-\methodwithref{no.uio.ifi.refaktor.extractors.ExtractAndMoveMethodPrefixesExtractor}{getSafePrefixes}
-method. The changer then choose the most suitable target by finding the most
-frequent occurring prefix among the safe ones. The target is the type of the
-first part of the prefix.
-
-After finding a suitable target, the \type{ExtractAndMoveMethodChanger} first
-creates an \type{ExtractMethodRefactoring} and performs it as explained in
-section \ref{executing_refactoring} about the execution of refactorings. Then it
-creates and performs the \type{MoveRefactoring} in the same way, based on the
-changes done by the Extract Method refactoring.
-
-\subsection{The ExtractAndMoveMethodPrefixesExtractor Class}
-This extractor extracts properties needed for building the Extract and Move
-Method refactoring. It searches through the given selection to find safe
-prefixes, and those prefixes form a base that can be used to compute possible
-targets for the move part of the refactoring. It finds both the candidates, in
-the form of prefixes, and the non-candidates, called unfixes. All prefixes (and
-unfixes) are represented by a
+class is a subclass of the class
+\typewithref{no.uio.ifi.refaktor.changers}{RefaktorChanger}. It is responsible
+for analyzing and finding the best target for, and also executing, a composition
+of the Extract Method and Move Method refactorings. This particular changer is
+the one of my changers that is closest to being a true LTK refactoring. It can
+be reworked to be one if the problems with overlapping changes are resolved. The
+changer requires a text selection and the name of the new method, or else a
+method name will be generated. The selection has to be of the type
+\typewithref{no.uio.ifi.refaktor.utils}{CompilationUnitTextSelection}. This
+class is a custom extension to
+\typewithref{org.eclipse.jface.text}{TextSelection}, that in addition to the
+basic offset, length and similar methods, also carry an instance of the
+underlying compilation unit handle for the selection.
+
+\subsubsection{The \type{ExtractAndMoveMethodAnalyzer}}
+The analysis and precondition checking is done by the
+\typewithref{no.uio.ifi.refaktor.analyze.analyzers}{ExtractAnd\-MoveMethodAnalyzer}.
+First is check whether the selection is a valid selection or not, with respect
+to statement boundaries and that it actually contains any selections. Then it
+checks the legality of both extracting the selection and also moving it to
+another class. If the selection is approved as legal, it is analyzed to find the
+presumably best target to move the extracted method to.
+
+For finding the best suitable target the analyzer is using a
+\typewithref{no.uio.ifi.refaktor.analyze.collectors}{PrefixesCollector} that
+collects all the possible candidates for the refactoring. All the non-candidates
+is found by an
+\typewithref{no.uio.ifi.refaktor.analyze.collectors}{UnfixesCollector} that
+collects all the targets that will give some kind of error if used. All prefixes
+(and unfixes) are represented by a
\typewithref{no.uio.ifi.refaktor.extractors}{Prefix}, and they are collected
-into prefix sets.\typeref{no.uio.ifi.refaktor.extractors.PrefixSet}.
-
+into sets of prefixes. The safe prefixes is found by subtracting from the set of
+candidate prefixes the prefixes that is enclosing any of the unfixes. A prefix
+is enclosing an unfix if the unfix is in the set of its sub-prefixes. As an
+example, \texttt{``a.b''} is enclosing \texttt{``a''}, as is \texttt{``a''}. The
+safe prefixes is unified in a \type{PrefixSet}. If a prefix has only one
+occurrence, and is a simple expression, it is considered unsuitable as a move
+target. This occurs in statements such as \texttt{``a.foo()''}. For such
+statements it bares no meaning to extract and move them. It only generates an
+extra method and the calling of it.
+
+\todoin{Clean up sections/subsections.}
+
+\subsubsection{The \type{ExtractAndMoveMethodExecutor}}
+If the analysis finds a possible target for the composite refactoring, it is
+executed by an
+\typewithref{no.uio.ifi.refaktor.change.executors}{ExtractAndMoveMethodExecutor}.
+It is composed of the two executors known as
+\typewithref{no.uio.ifi.refaktor.change.executors}{ExtractMethodRefactoringExecutor}
+and
+\typewithref{no.uio.ifi.refaktor.change.executors}{MoveMethodRefactoringExecutor}.
+The \type{ExtractAndMoveMethodExecutor} is responsible for gluing the two
+together by feeding the \type{MoveMethod\-RefactoringExecutor} with the
+resources needed after executing the extract method refactoring.
+\See{postExtractExecution}
+
+\subsubsection{The \type{ExtractMethodRefactoringExecutor}}
+This executor is responsible for creating and executing an instance of the
+\type{ExtractMethodRefactoring} class. It is also responsible for collecting
+some post execution resources that can be used to find the method handle for the
+extracted method, as well as information about its parameters, including the
+variable they originated from.
+
+\subsubsection{The \type{MoveMethodRefactoringExecutor}}
+This executor is responsible for creating and executing an instance of the
+\type{MoveRefactoring}. The move refactoring is a processor-based refactoring,
+and for the Move Method refactoring it is the \type{MoveInstanceMethodProcessor}
+that is used.
+
+The handle for the method to be moved is found on the basis of the information
+gathered after the execution of the Extract Method refactoring. The only
+information the \type{ExtractMethodRefactoring} is sharing after its execution,
+regarding find the method handle, is the textual representation of the new
+method signature. Therefore it must be parsed, the strings for types of the
+parameters must be found and translated to a form that can be used to look up
+the method handle from its type handle. They have to be on the unresolved
+form.\todo{Elaborate?} The name for the type is found from the original
+selection, since an extracted method must end up in the same type as the
+originating method.
+
+When analyzing a selection prior to performing the Extract Method refactoring, a
+target is chosen. It has to be a variable binding, so it is either a field or a
+local variable/parameter. If the target is a field, it can be used with the
+\type{MoveInstanceMethodProcessor} as it is, since the extracted method still is
+in its scope. But if the target is local to the originating method, the target
+that is to be used for the processor must be among its parameters. Thus the
+target must be found among the extracted method's parameters. This is done by
+finding the parameter information object that corresponds to the parameter that
+was declared on basis of the original target's variable when the method was
+extracted. (The extracted method must take one such parameter for each local
+variable that is declared outside the selection that is extracted.) To match the
+original target with the correct parameter information object, the key for the
+information object is compared to the key from the original target's binding.
+The source code must then be parsed to find the method declaration for the
+extracted method. The new target must be found by searching through the
+parameters of the declaration and choose the one that has the same type as the
+old binding from the parameter information object, as well as the same name that
+is provided by the parameter information object.
+
+
+\subsection{Finding the IMethod}\label{postExtractExecution}
+\todoin{Rename section. Write.}
+
+\subsection{Property collectors}
The prefixes and unfixes are found by property
collectors\typeref{no.uio.ifi.refaktor.extractors.collectors.PropertyCollector}.
-A property collector follows the visitor pattern \cite{dp} and is of the
-\typewithref{org.eclipse.jdt.core.dom}{ASTVisitor} type. An \type{ASTVisitor}
-visits nodes in an abstract syntax tree that forms the Java document object
-model. The tree consists of nodes of type
+A property collector follows the visitor pattern\citing{designPatterns} and is
+of the \typewithref{org.eclipse.jdt.core.dom}{ASTVisitor} type. An
+\type{ASTVisitor} visits nodes in an abstract syntax tree that forms the Java
+document object model. The tree consists of nodes of type
\typewithref{org.eclipse.jdt.core.do}{ASTNode}.
\subsubsection{The PrefixesCollector}
The \typewithref{no.uio.ifi.refaktor.extractors.collectors}{PrefixesCollector}
-is of type \type{PropertyCollector}. It visits expression
+finds prefixes that makes up tha basis for calculating move targets for the
+Extract and Move Method refactoring. It visits expression
statements\typeref{org.eclipse.jdt.core.dom.ExpressionStatement} and creates
prefixes from its expressions in the case of method invocations. The prefixes
found is registered with a prefix set, together with all its sub-prefixes.
\todo{Rewrite in the case of changes to the way prefixes are found}
-\subsubsection{The UnfixesCollector}
+\subsubsection{The UnfixesCollector}\label{unfixes}
The \typewithref{no.uio.ifi.refaktor.extractors.collectors}{UnfixesCollector}
-finds unfixes within the selection. An unfix is a name that is assigned to
-within the selection. The reason that this cannot be allowed, is that the result
-would be an assignment to the \type{this} keyword, which is not valid in Java.
-
-\subsubsection{Computing Safe Prefixes}
-A safe prefix is a prefix that does not enclose an unfix. A prefix is enclosing
-an unfix if the unfix is in the set of its sub-prefixes. As an example,
-\texttt{``a.b''} is enclosing \texttt{``a''}, as is \texttt{``a''}. The safe
-prefixes is unified in a \type{PrefixSet} and can be fetched calling the
-\method{getSafePrefixes} method of the
-\type{ExtractAndMoveMethodPrefixesExtractor}.
+finds unfixes within a selection. That is prefixes that cannot be used as a
+basis for finding a move target in a refactoring.
+
+An unfix can be a name that is assigned to within a selection. The reason that
+this cannot be allowed, is that the result would be an assignment to the
+\type{this} keyword, which is not valid in Java \see{eclipse_bug_420726}.
+
+Prefixes that originates from variable declarations within the same selection
+are also considered unfixes. This is because when a method is moved, it needs to
+be called through a variable. If this variable is also within the method that is
+to be moved, this obviously cannot be done.
+
+Also considered as unfixes are variable references that are of types that is not
+suitable for moving a methods to. This can be either because it is not
+physically possible to move the method to the desired class or that it will
+cause compilation errors by doing so.
+
+If the type binding for a name is not resolved it is considered and unfix. The
+same applies to types that is only found in compiled code, so they have no
+underlying source that is accessible to us. (E.g. the \type{java.lang.String}
+class.)
+
+Interfaces types are not suitable as targets. This is simply because interfaces
+in java cannot contain methods with bodies. (This thesis does not deal with
+features of Java versions later than Java 7. Java 8 has interfaces with default
+implementations of methods.) Neither are local types allowed. This accounts for
+both local and anonymous classes. Anonymous classes are effectively the same as
+interface types with respect to unfixes. Local classes could in theory be used
+as targets, but this is not possible due to limitations of the implementation of
+the Extract and Move Method refactoring. The problem is that the refactoring is
+done in two steps, so the intermediate state between the two refactorings would
+not be legal Java code. In the case of local classes, the problem is that, in
+the intermediate step, a selection referencing a local class would need to take
+the local class as a parameter if it were to be extracted to a new method. This
+new method would need to live in the scope of the declaring class of the
+originating method. The local class would then not be in the scope of the
+extracted method, thus bringing the source code into an illegal state. One could
+imagine that the method was extracted and moved in one operation, without an
+intermediate state. Then it would make sense to include variables with types of
+local classes in the set of legal targets, since the local classes would then be
+in the scopes of the method calls. If this makes any difference for software
+metrics that measure coupling would be a different discussion.
+
+\begin{listing}
+\begin{multicols}{2}
+\begin{minted}[]{java}
+// Before
+void declaresLocalClass() {
+ class LocalClass {
+ void foo() {}
+ void bar() {}
+ }
+
+ LocalClass inst =
+ new LocalClass();
+ inst.foo();
+ inst.bar();
+}
+\end{minted}
+
+\columnbreak
+
+\begin{minted}[]{java}
+// After Extract Method
+void declaresLocalClass() {
+ class LocalClass {
+ void foo() {}
+ void bar() {}
+ }
+
+ LocalClass inst =
+ new LocalClass();
+ fooBar(inst);
+}
+
+// Intermediate step
+void fooBar(LocalClass inst) {
+ inst.foo();
+ inst.bar();
+}
+\end{minted}
+\end{multicols}
+\caption{When Extract and Move Method tries to use a variable with a local type
+as the move target, an intermediate step is taken that is not allowed. Here:
+\type{LocalClass} is not in the scope of \method{fooBar} in its intermediate
+location.}
+\label{lst:extractMethod_LocalClass}
+\end{listing}
+
+The last class of names that are considered unfixes is names used in null tests.
+These are tests that reads like this: if \texttt{<name>} equals \var{null} then
+do something. If allowing variables used in those kinds of expressions as
+targets for moving methods, we would end up with code containing boolean
+expressions like \texttt{this == null}, which would not be meaningful, since
+\var{this} would never be \var{null}.
\subsection{The Prefix Class}
-\todo{?}
+This class exists mainly for holding data about a prefix, such as the expression
+that the prefix represents and the occurrence count of the prefix within a
+selection. In addition to this, it has some functionality such as calculating
+its sub-prefixes and intersecting it with another prefix. The definition of the
+intersection between two prefixes is a prefix representing the longest common
+expression between the two.
+
\subsection{The PrefixSet Class}
+A prefix set holds elements of type \type{Prefix}. It is implemented with the
+help of a \typewithref{java.util}{HashMap} and contains some typical set
+operations, but it does not implement the \typewithref{java.util}{Set}
+interface, since the prefix set does not need all of the functionality a
+\type{Set} requires to be implemented. In addition It needs some other
+functionality not found in the \type{Set} interface. So due to the relatively
+limited use of prefix sets, and that it almost always needs to be referenced as
+such, and not a \type{Set<Prefix>}, it remains as an ad hoc solution to a
+concrete problem.
+
+There are two ways adding prefixes to a \type{PrefixSet}. The first is through
+its \method{add} method. This works like one would expect from a set. It adds
+the prefix to the set if it does not already contain the prefix. The other way
+is to \emph{register} the prefix with the set. When registering a prefix, if the
+set does not contain the prefix, it is just added. If the set contains the
+prefix, its count gets incremented. This is how the occurrence count is handled.
+
+The prefix set also computes the set of prefixes that is not enclosing any
+prefixes of another set. This is kind of a set difference operation only for
+enclosing prefixes.
\subsection{Hacking the Refactoring Undo
History}\label{hacking_undo_history}
-\todo{Where to put this section?}
+\todoin{Where to put this section?}
As an attempt to make multiple subsequent changes to the workspace appear as a
single action (i.e. make the undo changes appear as such), I tried to alter
change\typeref{org.eclipse.ltk.core.refactoring.CompositeChange} that could be
added back to the manager. The interface of the undo manager does not offer a
way to remove/pop the last added undo change, so a possible solution could be to
-decorate \cite{dp} the undo manager, to intercept and collect the undo changes
-before delegating to the \method{addUndo}
+decorate\citing{designPatterns} the undo manager, to intercept and collect the
+undo changes before delegating to the \method{addUndo}
method\methodref{org.eclipse.ltk.core.refactoring.IUndoManager}{addUndo} of the
manager. Instead of giving it the intended undo change, a null change could be
given to prevent it from making any changes if run. Then one could let the
it is to complex to be easily manipulated.
+
+
+\chapter{Analyzing Code}
+
+\section{AST}
+\todoin{Explain what it is, or just how it is structured in Eclipse and how to
+analyze it?}
+
+\section{Illegal selections}
+
+\subsection{Not all branches end in return}
+
+\subsection{Ambiguous return statement}
+This problem occurs when there is either more than one assignment to a local
+variable that is used outside of the selection, or there is only one, but there
+are also return statements in the selection.
+
+\todoin{Explain why we do not need to consider variables assigned inside
+local/anonymous classes. (The referenced variables need to be final and so
+on\ldots)}
+
+\chapter{Eclipse Bugs Found}
+\todoin{Add other things and change headline?}
+
+\section{Eclipse bug 420726: Code is broken when moving a method that is
+assigning to the parameter that is also the move
+destination}\label{eclipse_bug_420726}
+This bug\footnote{\url{https://bugs.eclipse.org/bugs/show\_bug.cgi?id=420726}}
+was found when analyzing what kinds of names that was to be considered as
+\emph{unfixes} \see{unfixes}.
+
+\subsection{The bug}
+The bug emerges when trying to move a method from one class to another, and when
+the target for the move (must be a variable, local or field) is both a parameter
+variable and also is assigned to within the method body. Eclipse allows this to
+happen, although it is the sure path to a compilation error. This is because we
+would then have an assignment to a \var{this} expression, which is not allowed
+in Java.
+
+\subsection{The solution}
+The solution to this problem is to add all simple names that are assigned to in
+a method body to the set of unfixes.
+
+\section{Eclipse bug 429416: IAE when moving method from anonymous class}
+I
+discovered\footnote{\url{https://bugs.eclipse.org/bugs/show\_bug.cgi?id=429416}}
+this bug during a batch change on the \type{org.eclipse.jdt.ui} project.
+
+\subsection{The bug}
+This bug surfaces when trying to use the Move Method refactoring to move a
+method from an anonymous class to another class. This happens both for my
+simulation as well as in Eclipse, through the user interface. It only occurs
+when Eclipse analyses the program and finds it necessary to pass an instance of
+the originating class as a parameter to the moved method. I.e. it want to pass a
+\var{this} expression. The execution ends in an
+\typewithref{java.lang}{IllegalArgumentException} in
+\typewithref{org.eclipse.jdt.core.dom}{SimpleName} and its
+\method{setIdentifier(String)} method. The simple name is attempted created in
+the method
+\methodwithref{org.eclipse.jdt.internal.corext.refactoring.structure.\\MoveInstanceMethodProcessor}{createInlinedMethodInvocation}
+so the \type{MoveInstanceMethodProcessor} was early a clear suspect.
+
+The \method{createInlinedMethodInvocation} is the method that creates a method
+invocation where the previous invocation to the method that was moved was. From
+its code it can be read that when a \var{this} expression is going to be passed
+in to the invocation, it shall be qualified with the name of the original
+method's declaring class, if the declaring class is either an anonymous clas or
+a member class. The problem with this, is that an anonymous class does not have
+a name, hence the term \emph{anonymous} class! Therefore, when its name, an
+empty string, is passed into
+\methodwithref{org.eclipse.jdt.core.dom.AST}{newSimpleName} it all ends in an
+\type{IllegalArgumentException}.
+
+\subsection{How I solved the problem}
+Since the \type{MoveInstanceMethodProcessor} is instantiated in the
+\typewithref{no.uio.ifi.refaktor.change.executors}{MoveMethod\-RefactoringExecutor},
+and only need to be a
+\typewithref{org.eclipse.ltk.core.refactoring.participants}{MoveProcessor}, I
+was able to copy the code for the original move processor and modify it so that
+it works better for me. It is now called
+\typewithref{no.uio.ifi.refaktor.refactorings.processors}{ModifiedMoveInstanceMethodProcessor}.
+The only modification done (in addition to some imports and suppression of
+warnings), is in the \method{createInlinedMethodInvocation}. When the declaring
+class of the method to move is anonymous, the \var{this} expression in the
+parameter list is not qualified with the declaring class' (empty) name.
+
+\section{Eclipse bug 429954: Extracting statement with reference to local type
+breaks code}\label{eclipse_bug_429954}
+The bug\footnote{\url{https://bugs.eclipse.org/bugs/show\_bug.cgi?id=429954}}
+was discovered when doing some changes to the way unfixes is computed.
+
+\subsection{The bug}
+The problem is that Eclipse is allowing selections that references variables of
+local types to be extracted. When this happens the code is broken, since the
+extracted method must take a parameter of a local type that is not in the
+methods scope. The problem is illustrated in
+\myref{lst:extractMethod_LocalClass}, but there in another setting.
+
+\subsection{Actions taken}
+There are no actions directly springing out of this bug, since the Extract
+Method refactoring cannot be meant to be this way. This is handled on the
+analysis stage of our Extract and Move Method refactoring. So names representing
+variables of local types is considered unfixes \see{unfixes}.
+\todoin{write more when fixing this in legal statements checker}
+
+\chapter{Related Work}
+
+\section{The compositional paradigm of refactoring}
+This paradigm builds upon the observation of Vakilian et
+al.\citing{vakilian2012}, that of the many automated refactorings existing in
+modern IDEs, the simplest ones are dominating the usage statistics. The report
+mainly focuses on \emph{Eclipse} as the tool under investigation.
+
+The paradigm is described almost as the opposite of automated composition of
+refactorings \see{compositeRefactorings}. It works by providing the programmer
+with easily accessible primitive refactorings. These refactorings shall be
+accessed via keyboard shortcuts or quick-assist menus\footnote{Think
+quick-assist with Ctrl+1 in Eclipse} and be promptly executed, opposed to in the
+currently dominating wizard-based refactoring paradigm. They are ment to
+stimulate composing smaller refactorings into more complex changes, rather than
+doing a large upfront configuration of a wizard-based refactoring, before
+previewing and executing it. The compositional paradigm of refactoring is
+supposed to give control back to the programmer, by supporting \himher with an
+option of performing small rapid changes instead of large changes with a lesser
+degree of control. The report authors hope this will lead to fewer unsuccessful
+refactorings. It also could lower the bar for understanding the steps of a
+larger composite refactoring and thus also help in figuring out what goes wrong
+if one should choose to op in on a wizard-based refactoring.
+
+Vakilian and his associates have performed a survey of the effectiveness of the
+compositional paradigm versus the wizard-based one. They claim to have found
+evidence of that the \emph{compositional paradigm} outperforms the
+\emph{wizard-based}. It does so by reducing automation, which seem
+counterintuitive. Therefore they ask the question ``What is an appropriate level
+of automation?'', and thus questions what they feel is a rush toward more
+automation in the software engineering community.
+
+
\backmatter{}
\printbibliography
\listoftodos
git://git.uio.no / ifi-stolz-refaktor.git / blobdiff