Java Abstract Class

What is abstract class and why its needed ?

 
Abstract class is used when you don’t want to instantiate a class rather provide some common functionality that other classes can extend.
 
An abstract class can not be instantiated by itself.
 
An abstract class contain a mix of abstract and non-abstract methods.
 

Abstract class Example

 
Below is an example of such as abstract class.. the method printText() is abstract and the implemention is deferred to an overriding class.
 

package com.javatutorial;

public abstract class TestAbstractClass {
  public abstract void printText();
  public void setText() {
    System.out.println("Nonabstract method in Abstract class");
  }
}

 
Here is an example of child class extending the TestAbstractClass and implementing the abstract method printTest().

package com.javatutorial;

public class Hello extends TestAbstractClass {

  public static void main(String[] args) {
    Hello h =new Hello();
    h.setText();
    h.printText();
  }

  @Override
  public void printText() {
    System.out.println("Abstract method implement in child class");
  }

}

 
If you run this class, the output will be:

 

Nonabstract method in Abstract class
Abstract method implement in child class

 

Here are some rules about abstract classes :

 
– An abstract class can have non abstract methods. By putting non-abstract method in an abstract class, the concrete classes inherit the method implementation.
 
– An abstract class must be subclassed. So, you can not make a class both abstract and final.
 
– A class can implement one or more interfaces, but it can extend only one abstract class.
 

© 2015 – 2018, https:. All rights reserved. On republishing this post, you must provide link to original post