Java - Anonymous Classes

Java Anonymous Class

An anonymous class in Java is an inner class which is declared without any class name at all. In other words, a nameless inner class in Java is called an anonymous inner class. Since it does not have a name, it cannot have a constructor because we know that a constructor name is the same as the class name.

Use of Java Anonymous Inner Classes

Anonymous inner classes are used when you want to create a simple class that is needed for one time only for a specific purpose. For example, implementing an interface or extending a class.

Defining Anonymous Class in Java

You can define an anonymous inner class and create its object using the new operator at the same time in one step.

Syntax

The syntax of anonymous nested class is as follows −

new(argument-list){
   // Anonymous class body
}

Types of Anonymous Inner Classes in Java

• Anonymous inner class that extends a class

• Anonymous inner class that implements an interface

• Anonymous inner class as an argument

1. Anonymous inner class that extends a class

You can use an anonymous inner class to extend a class in Java.

Example: Anonymous inner class that extends a class

In the following example,we're using a new keyword to create an object of the anonymous inner class that has a reference of parent class type.

package com.tutorialspoint;

class Car {
   public void engineType() {
      System.out.println("Turbo Engine");
   }
}
public class Tester {
   public static void main(String args[]) {
      Car c1 = new Car();
      c1.engineType();
      Car c2 = new Car() {
         @Override
         public void engineType() {
            System.out.println("V2 Engine");
         }
      };
      c2.engineType();
   }
}

Output

If you compile and execute the above program, you will get the following result −

Turbo Engine
V2 Engine

2. Anonymous inner class that implements an interface

You can use an anonymous inner class to implement an interface in Java.

Example: Anonymous inner class that implements an interface

In the following example,we're using a new keyword to create an object of the anonymous inner class that has a reference of an interface type.

package com.tutorialspoint;

interface Software {
   public void develop();
}
public class Tester {
   public static void main(String args[]) {
      Software s = new Software() {
         @Override
         public void develop() {
            System.out.println("Software Developed in Java");
         }
      };
      s.develop();
      System.out.println(s.getClass().getName());
   }
}

Output

If you compile and execute the above program, you will get the following result −

Software Developed in Java
com.tutorialspoint.Tester$1

3. Anonymous inner class as an argument

We can use the anonymous inner class as an argument so that it can be passed to methods or constructors.

Example: Anonymous inner class as an argument

In the following example,we're passing an anonymous inner class as an argument to one method.

package com.tutorialspoint;

abstract class Engine {
   public abstract void engineType();
}
class Vehicle {
   public void transport(Engine e) {
      e.engineType();
   }
}
public class Tester {
   public static void main(String args[]) {
      Vehicle v = new Vehicle();
      v.transport(new Engine() {
         @Override
         public void engineType() {
            System.out.println("Turbo Engine");
         }
      });
   }
}

Output

If you compile and execute the above program, you will get the following result −

Turbo Engine