What are anonymous classes and where are they used?

An anonymous class is a local inner class without a name.

• Used in:

  • Creating event listeners in GUI applications (e.g., for buttons).
  • Implementing interfaces or extending abstract classes "on the spot" when only one instance is needed and its use is local.
  • In multithreading for creating instances of Runnable or Callable.

• Advantages:

  • Reduces code volume when a separate class reuse is not required.
  • Simplifies code reading for simple, one-time implementations.

• Disadvantages:

  • Can make code less readable for complex implementations.
  • Cannot be reused.
  • Access to outer class fields only through final or effectively final variables in older Java versions.

// Example of using an anonymous class for Runnable
Runnable myRunnable = new Runnable() {
    @Override
    public void run() {
        System.out.println("Running in an anonymous class thread.");
    }
};

new Thread(myRunnable).start();

// Example of using an anonymous class for an event listener (hypothetical)
// Some UI frameworks use this approach.
//button.setOnAction(new EventHandler<ActionEvent>() {
//    @Override
//    public void handle(ActionEvent event) {
//        System.out.println("Button clicked!");
//    }
//});