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%!TEX root = Programmierparadigmen.tex

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\chapter{Java}

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\index{Java|(}

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Im Folgenden wird in aller Kürze erklärt, wie man in Java Programme schreibt,

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die auf mehreren Prozessoren laufen.

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\section{Thread, ThreadPool, Runnable und ExecutorService}

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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

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\texttt{Interface Runnable}\xindex{Runnable}\\

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\-\hspace{0.8cm}$\leftharpoonup$ \texttt{java.lang.Thread}%

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\begin{itemize}

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    \item Methods:

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    \begin{itemize}

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        \item \texttt{void run()}: When an object implementing interface

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          Runnable is used to create a thread, starting the thread causes the

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          object's run method to be called in that separately executing thread.

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    \end{itemize}

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\end{itemize}

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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

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\texttt{Class Thread}\xindex{Thread}\\

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\-\hspace{0.8cm}$\leftharpoonup$ \texttt{java.lang.Thread}%

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\begin{itemize}

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    \item implements Runnable

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\end{itemize}

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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

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\texttt{Class ThreadPoolExecutor}\xindex{ThreadPoolExecutor}\\

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\-\hspace{0.8cm}$\leftharpoonup$ \texttt{java.util.concurrent.ThreadPoolExecutor}

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\begin{beispiel}[ExecutorService, Future\footnotemark]

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    \inputminted[numbersep=5pt, tabsize=4]{java}{scripts/java/executer-service-future-example.java}

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\end{beispiel}

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\footnotetext{WS 2013/2014, Kapitel 41, Folie 28}

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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

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\texttt{Interface Callable<V>}\xindex{Callable}\\

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\-\hspace{0.8cm}$\leftharpoonup$ \texttt{java.util.concurrent}

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\begin{itemize}

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    \item Parameter:

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    \begin{itemize}

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        \item \texttt{V} - the result type of method \texttt{call()}

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    \end{itemize}

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    \item Ermöglicht die Rückgabe von Ergebnissen

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 \end{itemize}

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\begin{beispiel}[Callable\footnotemark]

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    \inputminted[numbersep=5pt, tabsize=4]{java}{scripts/java/callable-example.java}

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\end{beispiel}

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\footnotetext{WS 2013/2014, Kapitel 41, Folie 27}

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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

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\section{Futures}\xindex{Future}\index{Promise|see{Future}}

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\enquote{Ein Future (engl. \enquote{Zukunft}) oder ein Promise (engl. \enquote{Versprechen}) bezeichnet in der Programmierung einen Platzhalter (Proxy) für ein Ergebnis, das noch nicht bekannt ist, meist weil seine Berechnung noch nicht abgeschlossen ist.}

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\texttt{Interface Future<V>}\xindex{Future}\\

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\-\hspace{0.8cm}$\leftharpoonup$ \texttt{java.util.concurrent}

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\begin{itemize}

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    \item \textbf{Parameter}:

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    \begin{itemize}

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        \item \texttt{V}: The result type returned by this Future's get method

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    \end{itemize}

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    \item Erlauben die Rückgabe von Ergebnissen

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\end{itemize}

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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

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\textbf{Beispiel}:

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% Zu lang, geht das kürzer?

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%\inputminted[numbersep=5pt, tabsize=4]{java}{scripts/java/matrix-multiplication.java}

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\begin{beispiel}[Runnable, ExecutorService, ThreadPool\footnotemark]

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    \inputminted[numbersep=5pt, tabsize=4]{java}{scripts/java/vorlesung-futures-basics.java}

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\end{beispiel}

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\footnotetext{WS 2013/2014, Kapitel 41, Folie 26}

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\section{Beispiele}

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Die folgenden Quelltexte wurden von Axel Busch erstellt.

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Das folgende Programm läuft in ca. 4min und $\SI{36}{\second}$ Sekunden auf einem Kern einer

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Intel Pentium P6200 CPU:

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\inputminted[linenos, numbersep=5pt, tabsize=4, frame=lines, label=SingleCorePrimeTest.java]{java}{scripts/java/SingleCorePrimeTest.java}

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Der folgende Code Testet das ganze mit mehreren Kernen auf einer Intel Pentium

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P6200 CPU:

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\inputminted[linenos, numbersep=5pt, tabsize=4, frame=lines, label=MultipleCorePrimeTest.java]{java}{scripts/java/MultipleCorePrimeTest.java}

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\begin{itemize}

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    \item 1 thread: 4min 38s

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    \item 2 threads: 3min 14s

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    \item 4 threads: 2min 44s

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    \item 8 threads: 2min 41s

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\end{itemize}

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\section{Literatur}

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\begin{itemize}

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    \item \href{http://openbook.galileocomputing.de/javainsel9/javainsel_14_004.htm}{Java ist auch eine Insel}: Kapitel 14 -

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          Threads und nebenläufige Programmierung

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    \item \href{http://www.vogella.com/tutorials/JavaConcurrency/article.html}{vogella.com}: Java concurrency (multi-threading) - Tutorial

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    \item Links zur offiziellen Java 8 Dokumentation:

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        \begin{itemize}

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            \item \href{http://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ThreadPoolExecutor.html}{ThreadPoolExecutor}

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            \item \href{http://docs.oracle.com/javase/8/docs/api/java/lang/Runnable.html}{Runnable}

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            \item \href{http://docs.oracle.com/javase/8/docs/api/java/lang/Thread.html}{Thread}

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            \item \href{http://docs.oracle.com/javase/8/docs/api/java/util/concurrent/Callable.html}{Callable}

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            \item \href{http://docs.oracle.com/javase/8/docs/api/java/util/concurrent/Future.html}{Future}

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        \end{itemize}

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\end{itemize}

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\index{Java|)}

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