abstract class java explained code example

Example 1: abstract class in java

Sometimes we may come across a situation where we cannot provide 
implementation to all the methods in a class. We want to leave the 
implementation to a class that extends it. In such case we declare a class
as abstract.To make a class abstract we use key word abstract. 
Any class that contains one or more abstract methods is declared as abstract. 
If we don’t declare class as abstract which contains abstract methods we get 
compile time error.
  
  1)Abstract classes cannot be instantiated
  2)An abstarct classes contains abstract method, concrete methods or both.
  3)Any class which extends abstarct class must override all methods of abstract
    class
  4)An abstarct class can contain either 0 or more abstract method.

Example 2: abstract class example in java

//abstract parent class
abstract class Animal{
   //abstract method
   public abstract void sound();
}
//Dog class extends Animal class
public class Dog extends Animal{

   public void sound(){
	System.out.println("Woof");
   }
   public static void main(String args[]){
	Animal obj = new Dog();
	obj.sound();
   }
}

Example 3: how to use an abstract class in java

interface methods{
    public void hey();
    public void bye();
}

//unable to implement all the abstract methods in the interface so 
// the other class automatically becomes abstract
abstract class other implements methods{
    public void hey(){
        System.out.println("Hey");
    }
}

//able to implement all the methods so is not abstract
class scratch implements methods {
    public void hey(){
        System.out.println("Hey");
    }
    public void bye() {
        System.out.println("Hey");
    }
}