136 lines
4.2 KiB
TeX
136 lines
4.2 KiB
TeX
\documentclass[a4paper]{article}
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\usepackage{graphicx}
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\usepackage[hidelinks]{hyperref}
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\usepackage[english]{babel}
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\usepackage{fancyhdr}
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\usepackage{listings}
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\usepackage{xcolor}
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\usepackage{float}
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\usepackage{lmodern}
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\usepackage[margin=2cm,top=2.5cm]{geometry}
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\hypersetup{pdfborder={0 0 0}}
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\usepackage[nomessages]{fp}
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\lstset{
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basicstyle=\small\ttfamily,
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%frame=shadowbox,
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rulesepcolor=\color{black},
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columns=fullflexible,
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commentstyle=\color{gray},
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keywordstyle=\color{blue},
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mathescape=true,
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aboveskip=1em,
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captionpos=b,
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abovecaptionskip=1em,
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belowcaptionskip=1em
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}
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\fancyhead[R]{Advanced Java Programming -- Assignment 2 -- Federico Lagrasta,
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Claudio Maggioni}
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\pagestyle{fancy}
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\begin{document}
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\begin{titlepage}
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\scshape
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\centering
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\includegraphics[width=3cm, keepaspectratio]{logo_usi.png}
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\par
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\vspace{0.1cm}
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\texttt{FACULTY OF INFORMATICS}
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\vspace{1cm}
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\raisebox{-\baselineskip}{\rule{\textwidth}{1px}}
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\rule{\textwidth}{1px}
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\vspace{0.2cm}
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{\LARGE{{ADVANCED JAVA PROGRAMMING}}}\par \vspace{0.1cm}
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Assignment 3
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\rule{\textwidth}{2px}
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\vspace{1cm}
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\begin{tabular}{lp{1cm}l}
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Author & \rule{0pt}{3ex} & FEDERICO \mbox{LAGRASTA}\\
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&&\\
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& \rule{0pt}{3ex} & CLAUDIO \mbox{MAGGIONI}\\
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\end{tabular}
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\vspace{1.3cm}
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\vfill
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\today
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\end{titlepage}
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\section*{A}
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\subsection*{1}
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The code will trigger a compile time error at line 14, since the variable
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\textit{z} cannot be used inside a lambda as it is not final or effectively
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final. This is because line 14 attempts to mutate the variable, thus making the
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variable not effectively final.
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\subsection*{2}
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The code will not compile.
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\section*{B}
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\subsection*{1}
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According to the contract satisfied by the \texttt{java.util.HashSet} class,
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there is no guarantee on the iteration order of the elements. Therefore,
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\texttt{set.stream()} evaluates to a stream whose ordering contractually does
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not reflect the order of the list. However, by analyzing the Java 17 standard
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library sources, given that:
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\begin{itemize}
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\item The elements of the source list are \textit{Integer}s and are already in natural order;
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\item \textit{HashSet} uses a \textit{HashMap} by encapsulation to store its elements;
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\item The \textit{Spliterator} returned by \textit{HashSet} is the \textit{Spliterator} over the keys
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of the backing \textit{HashHap};
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\item \textit{HashMap}'s spliterator implementation iterates over the key objects in the natural order
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of each object's hash code;
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\item \textit{Integer}'s \texttt{int hashCode()} implementation just returns the boxed \textit{int};
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\end{itemize}
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we can say that on any JVM this code is ran where the implementation of the
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standard library matches the sources provided with OpenJDK 17, we can say that
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in practice the \textit{Spliterator} backing the stream returned by
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\texttt{set.stream()} returns the elements in the correct order.
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However, the \texttt{java.util.stream} package
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documentation\footnote{\url{https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/util/stream/package-summary.html\#Ordering}},
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under the \textit{Ordering} section, explicitly mentions that the
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\textit{Stream} returned by an \textit{HashSet} is unordered. Therefore, also by
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the Stream API contract, we can say that the collection of this stream may
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result into a list that contractually is not in the order the elements were when
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creating the stream. However, in practice, since the created stream is
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sequential, the elements are kept in the given order as there is no performance
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advantage (unlike with parallel streams) in unordering them. Therefore,
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according to this contract, the method may throw a \textit{RuntimeException}
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even if this never happens in practice with any JVM with a standard library
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implementation matching the sources provided with OpenJDK 17.
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\marginpar[right text]{\color{white}\url{https://youtu.be/oqO-nlrZNbc}}
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\subsection*{2}
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What said in the previous section still applies, however in this case line 31
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makes the stream parallel, and since the stream is contractually unordered there
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is no guarantee the elements may be collected in order since the stream API
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implementation may not follow the original ordering for parallelization
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performance reasons.
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\end{document}
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