Anonymous Code

[Zaid]

I recently encountered a code in my java program that is as follows..

button.addActionListener(new ActionListener() {
   public void actionPerformed(ActionEvent e)
   {
      //Some action here
   }
});

I don't know what is after new ActionListener() but it seems a method of ActionListener is overridden and in some block....huh

[Fou-Lu]

Yeah, this is an anonymous inner class. ActionListener itself is an interface, but since it is being invoked and the entire method set is being declared as a part of the class body, this is valid code. Prior to Java 8, it's also the closest thing we have to a closure in Java.
So effectively you create an unnamed instance and provide that as the argument. That particular instance can never be used again.