Double Brace Initialisation
This is a Java trick which involves creating an anonymous class with an initialiser block, eg.
new Object() {{ // Initialisation stuff here }};
It's especially useful for collections:
List<Integer> list = new ArrayList<Integer>() {{ add(1); add(2); add(3); add(4); add(5); }}; System.out.println(list);
Map<Integer, String> map = new HashMap<Integer, String>() {{ put(1, "one"); put(2, "two"); put(3, "three"); put(4, "four"); put(5, "five"); }}; System.out.println(map);
But can also be useful in GUI programming:
JFrame frame = new JFrame() {{ setDefaultCloseOperation(EXIT_ON_CLOSE); add(new JLabel("Hello, World!")); pack(); }}; frame.setVisible(true);
Be careful when using this, however, because any object created using double brace initialisation belongs to an anonymous subclass, not the original class.