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

Consider the below example

public class ClastingDemo {

/**
 * @param args
 */
public static void main(String[] args) {
    AOne obj = new Bone();
    ((Bone) obj).method2();
}
}

class AOne {
public void method1() {
    System.out.println("this is superclass");
}
}


 class Bone extends AOne {

public void method2() {
    System.out.println("this is subclass");
}
}

here we create the object of subclass Bone and assigned it to super class AOne reference and now superclass reference does not know about the method method2 in the subclass i.e Bone during compile time.therefore we need to downcast this reference of superclass to subclass reference so as the resultant reference can know about the presence of methods in the subclass i.e Bone