how to make abstract method code example

Example 1: is it necessary for abstract class to have abstract method

No, abstract class can have zero abstract methods.

Example 2: how to create an abstract method in java

abstract class Scratch{
  // cannot be static
    abstract public void hello();
    abstract String randNum();
}

interface Other{
  //all methods in an interface are abstract
    public void bye();
    String randDouble();
}