Core Java - SPLessons
SPLessons 5 Steps, 3 Clicks
5 Steps - 3 Clicks

Java Interface

Java Interface

shape Description

Java Interface, As discussed in the previous chapter interface is used to get full abstraction , to solve the problem of multiple Inheritance, and by default interface is an abstraction. Java interface also follows IS-A relationship. The main advantage of the interface is to get the loose coupling. Following some points needs to be remember.

shape Conceptual figure

A class can implement the interface.

shape Example

[java] interface printable{ void print(); } class splesson implements printable{ public void print(){System.out.println("Hello Splesson.");} public static void main(String args[]){ splesson obj = new splesson(); obj.print(); } } [/java] Where printable is an interface and it has only one method that is print(). [java]interface printable{ void print();}[/java] Output: When compile the code the result will be as follows. [c] Hello Splesson. [/c]

shape Example

[java] package com.spl.absI; public class AbstractInterface { public static void main(String[] args) { System.out.println("Program starts"); DerivedClass dref=new DerivedClass(); dref.test1(); dref.test2(); System.out.println("Program ends"); } } interface Sample1 { void test1(); void test2(); } abstract class A implements Sample1 { public void test1() { System.out.println("test1() method"); } } class DerivedClass extends A { @Override public void test2() { // TODO Auto-generated method stub System.out.println("test2() method"); } } [/java] Output: When compile the program following is the output will be displayed. [c] Program starts test1() method test2() method Program ends [/c]


shape Description

An Java Interface can inherit from another interface using "extends" keyword. Following is the syntax. [java]interface Sample1{ void test1(int a); } interface Sample2 extends Sample1{ void test2(); }[/java]

Interface and inheritance

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A class can implement more than one interface at a time. In this case, the class has to provide definition for all the methods of each interface. A class can inherit from another class and implements more than one interface. For more detailed overview on inheritance click here .

shape Syntax

Class DerivedClass extends Baseclass implements Interface1,Interface2 { }

shape Example

[java] package com.spl.concrete; public class Interface3 { public static void main(String[] args) { System.out.println("Program starts"); B dref=new B(); dref.test1(); System.out.println("Program ends"); } } class BaseClass { public void test1() { System.out.println("Running test1() mehod"); } } interface Sample1 { void test1(); } class B extends BaseClass implements Sample1 { //inheriting from both Sample1 and BaseClass } [/java] In the above example, the class B is becoming concrete because the test 1() method inherited from base class is full filling the contract of Sample 6 interface. Output: [c] Program starts Running test1() method Program ends[/c]

shape Example

[java] package com.spl.int4; public class Interface4 { public static void main(String[] args) { System.out.println("Program starts"); E dref=new E(); dref.test1(); System.out.println("Program ends"); } } interface Sample7 { void test1(); } interface Sample8 { void test1(); } class E implements Sample7,Sample8 { @Override public void test1() { // TODO Auto-generated method stub System.out.println("Running test1() method"); } } [/java] In the above example, the class is becoming concrete by overriding only test1() method.The overrided method fulfills the contract of both Sample 7 & Sample 8 interface,because the method signature are same. Output: When compile the code output will be as follows. [c] Program starts Running test1() method Program ends [/c]

Multiple Inheritance By Using Interface

The following is an example to achieve multiple inheritance by using interface. [java]package com.splessons; interface Printable{ void print(); } interface Showable{ void show(); } class Splesson implements Printable,Showable{ public void print(){System.out.println("Hello");} public void show(){System.out.println("Welcome To Splessons");} public static void main(String args[]){ Splesson obj = new Splesson(); obj.print();; } } [/java] In the above example, Printable and Showable are the two interfaces that have their own methods and where Splesson is the class name that implements two interfaces(there is no ambiguity). Output: [java]Hello Welcome To Splessons[/java]

Advantages of interfaces

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The following are the some advantages of interfaces.


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  • Multiple inheritance problem will be done by interface.
  • 100% of abstraction will be achieved through an interface.