  Den perfekte julegaven til Javakoden din Johannes Brodwall Steria

  Wednesday, November 18th, Mark Reinhold from Sun announced that it was time for closures in Java.

  This came as a surprise to everyone, but what was announced?

  Hvorfor closures? Bygg bedre bibliotek.

  Eksempel: Lese alle linjer i fil

  void theOldWay(String[] args) throws IOException { BufferedReader reader = null; boolean done = false; try { FileReader filerdr = new FileReader(new File(args[0])) reader = new BufferedReader(fdr); String line; while ( (line = reader.readLine()) != null) { System.out.println("This is a line:" + line); } done = true; } finally { if (reader != null) { try { reader.close(); } catch (IOException e) { if (done) throw e; } } }

  Er dette rettferdig?

  void theNewWay(String fname) throws IOException { forEachLine( new File( fname), #(String line) { System.out.println("This is a line:" + line); }); }

  void theNewWay(String[] args) throws IOException { forEachLine( new File( args[0]), #(String line) { System.out.println("This is a line:"+line); }); }

  Å bygge en funksjon som tar closures

  public interface LineCallback { public void doForLine(String line) throws IOException; } public static void forEachLine(File file, final LineCallback lineCallback) throws IOException { doWithFile(file, #(Reader reader) { // … lineCallback.doForLine(line); } }); }

  Hva er greia med disse #’ene?

  OriginClass origin = new OriginClass(); origin.setBar("bar on origin"); TargetClass target = new TargetClass(); mapField( origin, OriginClass#bar, target, TargetClass#foo); System.out.println(target.getFoo());

  OriginClass origin = new OriginClass(); origin.setBar("bar on origin"); TargetClass target = new TargetClass(); mapField( origin, OriginClass#bar, target, TargetClass#foo); System.out.println(target.getFoo());

  OriginClass#bar Person#setSalary(int) #(String line) { System.out.println("This is a line:" + line); }

  Fem ting du bør bruke closures til

  Hva gjør vi for å komme rundt et dårlig språk

  Funksjoner som frigir ressurser Interne iteratorer Asynkrone kall Callbacks Queries

  Closures lar oss bygge bedre bibliotek.

  Her kan du lære mer: (Implementasjon) the-language/ the-language/

  Johannes Brodwall Chief Scientist Steria, Norway Takk for oppmerksomheten 