Curly braces in "new" expression? (e.g. "new MyClass() { ... }")

This is the syntax for creating an instance of anonymous class that extends Handler. This is part of Java.

This is happned when you create the instance reference of the Interface.For example I want to create the instance of the interface Runnable with the class, then I can create it by creating an anonymous class for the same and override the run() method of the interface. You can understand well by looking at the another example other then you stated below.

Runnable runnable = new Runnable() {    public void run() {        // TODO Auto-generated method stub    }};

Instantiates & returns reference of an anonymous subclass of current class.

new Handler() {};

It is as equal as extending the Handler class explicitly but it requires name specification obviously of subclass & so it will not remain anonymous any longer.

class Main{    int a = 5;    void func(){}    void meth(){        Main ref2 = new Main() {            void func(){                System.out.println(a);            }                   };        ref2.func();    }        public static void main(String[] args) {        Main mm = new Main();        mm.meth();    }}//5