Java SE 8 or JDK1.8 Interface features

Added/upgraded default/static methods

What was the issue in java Interface in earlier version?

1  All abstract methods need to implement in implementation class.

        

   If we add any additional abstract method in existing interface then  need to implement in implementation classes, everywhere else  compilation issue

3   

   All binary and dependency need to recompile and again build for it 

All issue got resolved by adding the default/static methods in Interface

Will see only by one examples.

Writing on basis of below software's

1. JDK1.8
2. Eclipse
3. Windows OS
4. Basic knowledge of java

Verify the JDK installation

Open the command prompt and verify the java installation
Type the 
C:\>javac -version
javac 1.8.0_74

C:\>java -version
java version "1.8.0_74"

Now java installation got verified, as installed JDK1.8.0_74

Verify the Eclipse installation

Go the the installation directory of eclipse and click on the eclipse.exe

e.g C:\eclipse\eclipse-java-mars-1-win32\eclipse\eclipse.exe

Create the new java project in Eclipse

Open the eclipse
File
New
Java project
Type the project name: Interface_In_Java_Programming_JavaSE_8_JDK1.8
Next
Finish

Java project created in eclipse with directory structure:
 Interface_In_Java_Programming_JavaSE_8_JDK1.8
     - src
     - JRE System Library

How to create Interface in eclipse? 

Right click on the src folder under Interface_In_Java_Programming_JavaSE_8_JDK1.8
project
New
Interface
Type the package name: com.atozexamples
Type the name: Calculator
Finish

Calculator.java

package com.atozexamples;

public interface Calculator {

}

Note: Above code are also called tag interface (also called a marker interface) in java, good examples is java.io.Serializable.

public interface Serializable {

}

Calculator interface with default and static method with declaration and implementation.


Calculator.java

package com.atozexamples.jdk8;

public interface Calculator {

       // Abstract method, This method need to

       // implement in implementation calss

       void display();

       // Abstract method, This method need

       // to implement in implementation calss

       void print();

       /**

        * Default method in interface with implementation, 

        * not required to

        * implement in implementation class

        */

       default int addition(int a, int b) {

         System.out.println("Calculator interface Addition result "       + a + b);

              return a + b;

       }

       /**

        * static method in interface with implementation, 

        * not required to implement

        * in implementation class

        */

       static int sub(int a, int b) {

              int c = a - b;

            System.out.println("Calculator interface sub result " 

            + c);

              return c;

       }

}

SimpleCalculator class implements Calculator interface and override the display() and print() methods where as calls addition() default method and Calculator.sub() static method.

SimpleCalculator.java

package com.atozexamples.jdk8;

public class SimpleCalculator implements Calculator {

       public SimpleCalculator() {

       }

       @Override

       public void display() {

              System.out.println("Displaying the imp cls!");

       }

       @Override

       public void print() {

              System.out.println("Printing the impl cls");

       }

       public static void main(String[] args) {

              SimpleCalculator obj = new SimpleCalculator();

              // For calling the default method

              obj.addition(10, 20);

              obj.display();

              obj.print();

              // Calling the static method defined in interface by

              // interface name instead of object class

              Calculator.sub(10, 20);

              obj.display();

              obj.print();

       }

}

We can't call obj.sub(,) method wont be possible.

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Happy learning and implementation