How to implement an interface using an anonymous inner class in Java?

What is an Anonymous Inner Class

In Java, an anonymous inner class is a class that doesn't have a name, we will directly define it at the time of instantiation. You can use it in cases where you need to override methods of a class (or interface) only once, without creating a separate named class.

Syntax of Anonymous Inner Class

When you are using a class to create an anonymous inner class in Java, use the following syntax:

Class objectName = new Class() {
    // Override necessary methods
};

When you are implementing an interface using an anonymous inner class in Java, use the syntax given below:

Interface objectName = new Interface() {
    // Override necessary methods
};

Implementing Interface using Anonymous Inner Class

An Interface is a type of class that is defined using the keyword interface. To access its members within a class, we need to use the implements keyword while defining that class. However, you can implement it using an anonymous inner class just by overriding the interface's methods without creating a separate named class.

Example

In the following Java program, we implement the combustion() method of the Oxygen interface using an anonymous inner class and print its output statement.

// interface Oxygen
interface Oxygen {
   void combustion();
}
public class CO2 {
   public static void main(String[] args) {
      // implementing Oxygen using anonymous inner class
      Oxygen fire = new Oxygen() {
         @Override
         public void combustion() {
            System.out.println("Fire needs Oxygen and produces CO2!");
         }
      };
      // Calling the implemented method
      fire.combustion();
   }
}

On running the above code, it will display the following output:

Fire needs Oxygen and produces CO2!