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In this post, we will look at a program to demonstrate default methods in Interfaces in Java 8.
- Default methods are introduced in Java 8 to provide a default implementation for methods in an Interface.
- Using this feature, new functionality can be added to the existing interfaces without breaking the code.
- “default” keyword is specified while providing the implementation for a method in an Interface.
Let’s look at an example program:
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package com.clearurdoubt; /** * * @author Sai Gowtham Badvity * Default Method Implementation demo in Java 8 * */ interface IA { // Normal abstract method void someIAMethod(); // Default method implementation in IA default void doSomething() { System.out.println("This is a default implementation of doSomething() in IA."); } } interface IB extends IA { // Normal abstract method void someIBMethod(); // Default method implementation in IB default void doSomething() { //IA.super.doSomething(); // This statement plays an important role System.out.println("This is a default implementation of doSomething() in IB."); } } class AB implements IA, IB // AB implements both the interfaces { @Override public void someIAMethod() // IA specific method implementation { System.out.println("someIAMethod() method implementaion."); } @Override public void someIBMethod() // IB specific method implementation { System.out.println("someIBMethod() method implementaion."); } } // Let's see the default method implementation feature public class DefaultMethodDemo { public static void main(String[] args) { IA referenceIA = new AB(); IB referenceIB = new AB(); // Output of below method calls are normal as per the expectation referenceIA.someIAMethod(); referenceIB.someIBMethod(); // The output of the below methods will be interesting. referenceIA.doSomething(); referenceIB.doSomething(); } } |
Output:
Instead of specialized behavior, if the child interface wants to use its parent default method implementation, below syntax is used:
<ParentInterfaceName>.super.<methodName>();
So if we comment the line 32 and uncomment line 31 in the above program, the output would be:
Happy Learning :).
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