utilities.tex

\section{Hilfsfunktionen}

\begin{frame}[fragile]
  \frametitle{Hilfsfunktionen für Listen}

  \begin{block}{java.util.Collections.emptyList()}
    \begin{lstlisting}
      List<String> l = Collections.emptyList();
    \end{lstlisting}
  \end{block}

  \pause
  
  \begin{block}{com.google.common.collect.Lists.newArrayList(T...)}
    \begin{lstlisting}
      List<String> l = Lists.newArrayList("a", "b", "c", "d");
    \end{lstlisting}
  \end{block}

  \pause
  
  \begin{block}{java.util.AbstractList.subList(int, int)}
    from-index inklusiv, to-index exklusiv
    \begin{lstlisting}
      List<String> l = ...
      List<String> sub = l.subList(2,5);
    \end{lstlisting}
  \end{block}
  
  \pause
  
  \begin{block}{java.util.Collections.unmodifiableList(List\textless? extends T\textgreater)}
    \begin{lstlisting}
      Collections.unmodifiableList(list).add("a"); // wirft UnsupportedOperationException
    \end{lstlisting}
  \end{block}

\end{frame}

\begin{frame}[fragile]
  \frametitle{Hilfsfunktionen für Listen}

  \begin{block}{java.util.Collections.singletonList(T)}
    \begin{lstlisting}
      List<String> list = Collections.singletonList("a");
    \end{lstlisting}
  \end{block}
  
  \pause
  
  \begin{block}{java.util.Collections.synchronizedList(List\textless T\textgreater)}
    erzeugt eine synchronisierte List
    \begin{lstlisting}
      List<String> l = ...
      List<String> s = Collections.synchronizedList(l);
    \end{lstlisting}
  \end{block}

\end{frame}



%%%%%%%%%%%%%%%%%%%
%      Map        %
%%%%%%%%%%%%%%%%%%%

\begin{frame}[fragile]
  \frametitle{Hilfsfunktionen für Maps}

  \begin{block}{java.util.Collections.synchronizedMap(Map\textless K, V\textgreater)}
    erzeugt eine synchronisierte Map
    \begin{lstlisting}
      Map<String, String> m = ...
      Map<String, String> s = Collections.synchronizedMap(m);
    \end{lstlisting}
  \end{block}
  
  \pause

  \begin{block}{java.util.Collections.unmodifiableMap(Map\textless K, V\textgreater)}
    \begin{lstlisting}
      Map<String, String> unmodifiableMap = Collections.unmodifiableMap(map);
      unmodifiableMap.put("a", "b"); // UnsupportedOperationException
    \end{lstlisting}
  \end{block}

  \pause
  
  \begin{block}{java.util.Collections.emptyMap()}
    unmodizierbare, leere Map
    \begin{lstlisting}
      Map<String, String> empty = Collections.emptyMap();
      empty.put("a", "b");// UnsupportedOperationException
    \end{lstlisting}
  \end{block}

\end{frame}
  
\begin{frame}[fragile]
  \frametitle{Hilfsfunktionen für Maps}
  
  \begin{block}{java.util.Collections.singletonMap(K, V)}
    unmodizierbare, ein-elementige Map
    \begin{lstlisting}
      Map<String, String> single = Collections.singletonMap("a", "b");
      single.put("a", "b");// UnsupportedOperationException
    \end{lstlisting}
  \end{block}
  
\end{frame}

\begin{frame}[fragile]
  \frametitle{Hilfsfunktionen für Maps}

  \begin{block}{java.util.Map.computeIfAbsent(K, Function\textless ? super K, ? extends V\textgreater)}
    füge in eine existierende Liste ein, ggf. erzeuge diese Liste
    \begin{lstlisting}
    void addOld(Map<String, List<String>> map, String key, String value) {
        List<String> list = map.get(key);
        if (list == null) {
            list = new ArrayList<>();
            map.put(key, list);
        }
        list.add(value);
    }
      \end{lstlisting}
      \pause
      \begin{lstlisting}
    void addNew(Map<String, List<String>> map, String key, String value) {
        map.computeIfAbsent(key, x -> new ArrayList<>()).add(value);
    }
    \end{lstlisting}
  \end{block}

\end{frame}

\begin{frame}[fragile]
  \frametitle{Hilfsfunktionen für Maps}

  \begin{block}{java.util.Map.getOrDefault(Object, V)}
    default value in Map
    \begin{lstlisting}
            // alt
            Map<String, String> map = new HashMap<>();
            String s = map.get("a");
            if (s == null) {
                s = "default";
            }
            System.out.println(s);
      \end{lstlisting}
      \pause
      \begin{lstlisting}
            Map<String, String> map = new HashMap<>();
            map.put("a", "a");
            System.out.println(map.getOrDefault("a", "default"));
            System.out.println(map.getOrDefault("b", "default"));
    \end{lstlisting}
  \end{block}

\end{frame}