how to create an abstract method in java

1Sometimes we may come across a situation where we cannot provide 
2implementation to all the methods in a class. We want to leave the 
3implementation to a class that extends it. In such case we declare a class
4as abstract.To make a class abstract we use key word abstract. 
5Any class that contains one or more abstract methods is declared as abstract. 
6If we don’t declare class as abstract which contains abstract methods we get 
7compile time error.
8  
9  1)Abstract classes cannot be instantiated
10  2)An abstarct classes contains abstract method, concrete methods or both.
11  3)Any class which extends abstarct class must override all methods of abstract
12    class
13  4)An abstarct class can contain either 0 or more abstract method.    

1abstract class scratch{
2  
3}

1abstract class Scratch{
2  // cannot be static
3    abstract public void hello();
4    abstract String randNum();
5}
6
7interface Other{
8  //all methods in an interface are abstract
9    public void bye();
10    String randDouble();
11}