Java 8 Default Methods

by Online Tutorials Library July 14, 2022

Java Default Methods

Java provides a facility to create default methods inside the interface. Methods which are defined inside the interface and tagged with default are known as default methods. These methods are non-abstract methods.

Java Default Method Example

In the following example, Sayable is a functional interface that contains a default and an abstract method. The concept of default method is used to define a method with default implementation. You can override default method also to provide more specific implementation for the method.

Let’s see a simple

 interface Sayable{ // Default method  default void say(){ System.out.println(“Hello, this is default method”); } // Abstract method void sayMore(String msg); } public class DefaultMethods implements Sayable{ public void sayMore(String msg){// implementing abstract method  System.out.println(msg); } public static void main(String[] args) { DefaultMethods dm = new DefaultMethods(); dm.say();// calling default method dm.sayMore(“Work is worship”);// calling abstract method  } } 

Output:

Hello, this is default method Work is worship

Static Methods inside Java 8 Interface

You can also define static methods inside the interface. Static methods are used to define utility methods. The following example explain, how to implement static method in interface?

 interface Sayable{       // default method       default void say(){           System.out.println(“Hello, this is default method”);       }       // Abstract method       void sayMore(String msg);       // static method       static void sayLouder(String msg){           System.out.println(msg);       }   }   public class DefaultMethods implements Sayable{       public void sayMore(String msg){     // implementing abstract method           System.out.println(msg);       }       public static void main(String[] args) {           DefaultMethods dm = new DefaultMethods();           dm.say();                       // calling default method           dm.sayMore(“Work is worship”);      // calling abstract method           Sayable.sayLouder(“Helloooo…”);   // calling static method       }   }   

Output:

Hello there Work is worship Helloooo...

Abstract Class vs Java 8 Interface

After having default and static methods inside the interface, we think about the need of abstract class in Java. An interface and an abstract class is almost similar except that you can create constructor in the abstract class whereas you can’t do this in interface.

 abstract class AbstractClass{       public AbstractClass() {        // constructor           System.out.println(“You can create constructor in abstract class”);       }       abstract int add(int a, int b); // abstract method       int sub(int a, int b){      // non-abstract method           return a-b;       }       static int multiply(int a, int b){  // static method           return a*b;       }   }   public class AbstractTest extends AbstractClass{       public int add(int a, int b){        // implementing abstract method           return a+b;       }       public static void main(String[] args) {           AbstractTest a = new AbstractTest();           int result1 = a.add(20, 10);    // calling abstract method           int result2 = a.sub(20, 10);    // calling non-abstract method           int result3 = AbstractClass.multiply(20, 10); // calling static method           System.out.println(“Addition: “+result1);           System.out.println(“Substraction: “+result2);           System.out.println(“Multiplication: “+result3);       }   }   

Output:

You can create constructor in abstract class Addition: 30 Substraction: 10 Multiplication: 200

Next TopicJava 8 forEach

Java 8 Default Methods

Java Default Methods

Java Default Method Example

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Abstract Class vs Java 8 Interface

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