Abstract Class and Abstract Method

abstract class Base
{
    private int roll;
    private String name;
    private String branch;
    
    Base(int roll,String name,String branch)
    {
        this.roll=roll;
        this.name=name;
        this.branch=branch;
    }
    int getRoll()
    {
        return roll;
    }
    String getName()
    {
        return name;
    }
    String getBranch()
    {
        return branch;
    }
    abstract void display();   // abstract Method
}
class Child extends Base
{
    Child(int roll,String name,String branch)
    {
        super(roll,name,branch);   
    }
    void display()
    {
      System.out.println("Name is : "+getName());
      System.out.println("Roll number is : "+getRoll());
      System.out.println("Branch is : "+getBranch());
    }
}

class MainClass
{
    public static void main(String[] args)
    {
        Base b=new Child(21,"sanjay","cse");  //upcasting
        b.display();
    }
}

Output