" casting in java "

Question

Hi All,
Can some one help me find out whats the error in my code??
what/where is wrong in my casting??
import java.lang.* ;
class base {
public void display()
System.out.println( " i am in base ");
class derv extends base{
public void show()
System.out.println( " i am in derv ");
class test13 {
public static void main(String args[]) throws ClassCastException {
base Obj1 = new base();
base Obj2 = new derv();
derv Obj3 = new derv();
//derv Obj4 = new base();//not valid
Obj1.display();// regular
Obj2.display();
Obj3.display();
Obj3.show();// regular
derv Obj4 = new derv();
Obj4 = (derv) Obj1;
Obj4.show();
derv Obj5 = new derv();
Obj5 = (derv) Obj2;
Obj5.show();
};i am getting a run time exception like this :
C:\JAVAEX~1\test>java test13
i am in base
i am in base
i am in base
i am in derv
Exception in thread "main" java.lang.ClassCastException: base
at test13.main(test13.java:37)
Thank you very much in advance..
Thanks and regards,

Answer 1

The cast cast occured because you tried an downcast.
may be this could help
public class A1{
     A1(){
          A1 a=new A1();
          B1 b=new B1();
          //up cast...
          A1 a1=b;// no need of explisit cast
          //down cast          
           /*explisit cast requires..may throw exception, if a is not an instance of B1..
          ie. it will thorow excpetion in this case*/
          B1 b1=(B1)a;
          //example of not throwing excpetion..
          B1 b2=(B1)a1;
class B1 extends A1{