Abstract Class and Interface in Java - A Beginner's Guide

Abstract Class in Java

Class declared with Abstract keyword is known as abstract class in java.  This abstract class have abstract and non-abstract methods. Basically abstract is a process of hiding the properties and showing only functionality to the user. It shows only important things to the user and hides the internal details.

abstract class ClassOne
{
abstract public void method();
public void method1()
{
System.out.println("Method");
}
}
class ClassTwo extends ClassOne
{
public void method()
{
System.out.println("Method 2");
}
}

Interfaces in Java

It is not a class, all methods declared in this block are incomplete. Interface block should be declared with ‘interface’ keyword.  Interface is a blueprint of class. Java core part and a way to achieve data  abstraction in java along with abstract class.  Multiple interface implementation allows to implemented subclass. It is fully abstract class. Here no need to declare abstract keyword and no need to declare interface keyword for all methods.  Let see the example.

interface Program1
{
public void method1();
}
class MyProgram1 implements Program1
{
public void method1()
{
System.out.println("hello this is overrided method..");
}
}

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Difference between Abstract class and Interface in Java