GRAYGER

A few days ago, I registered stackoverflow.com and found an interesting post: what are hidden features of Java?

The stuffs that I didn’t know before are

• Double brace initialization

	Map map=new HashMap<String,String>() {
		{
			put("key1","value1");
			put("key2","value2");
		}
	};

• Instance initializer

public class Initializer {
	static {
		System.out.println("static");
	}
	{
		System.out.println("instance");
	}
	public Initializer() {
		System.out.println("constructor");
	}
}

• Covariant return type

	abstract class Base {
		abstract List getList();
	}

	class Sub extends Base {
		@Override
		ArrayList getList() {
			return null;
		}
	}

Double brace initialization uses instance initializer because first brace is for declairing annomymous inner class and second brace is for instance initializer block.