Downcasting in Java

Question

Upcasting is allowed in Java, however downcasting gives a compile error.

The compile error can be removed by adding a cast but would anyway break at the runtime.

Answer 1

@ Original Poster - see inline comments.

public class demo 
{
    public static void main(String a[]) 
    {
        B b = (B) new A(); // compiles with the cast, but runtime exception - java.lang.ClassCastException 
        //- A subclass variable cannot hold a reference to a superclass  variable. so, the above statement will not work.

        //For downcast, what you need is a superclass ref containing a subclass object.
        A superClassRef = new B();//just for the sake of illustration
        B subClassRef = (B)superClassRef; // Valid downcast. 
    }
}

class A 
{
    public void draw() 
    {
        System.out.println("1");
    }

    public void draw1() 
    {
        System.out.println("2");
    }
}

class B extends A 
{
    public void draw() 
    {
        System.out.println("3");
    }

    public void draw2() 
    {
        System.out.println("4");
    }
}