Object reference casting

[Vedhas Pitkar]

Hi ALL!I am a little bit confused over object reference casting.Help me out guys ,my deadline is approaching!
class A {
void method(){
System.out.println(" in A");
}
}
class B extends A {
void method(){
System.out.println(" in B");
}
}
class C extends B {
void method(){
System.out.println(" in C");
}
}
public class MyClass{
public static void main(String args[]){
A a=new C();
B b=(B)a;
b.method();//prints "in C" no problem here
C c=new C();
b=c;// shouldn't this give me a compiler or runtime error??
if(b instanceof C)
System.out.println("true");// this prints true why?
}

}
Do let me know.
Thanks all,
Vedhas.

[swati bannore]

Hey, even i got confused.. i just tried more instanceof conditions and it all seem to be true.. !

class A {
void method(){
System.out.println(" in A");
}
}
class B extends A {
void method(){
System.out.println(" in B");
}
}
class C extends B {
void method(){
System.out.println(" in C");
}
}
public class MyClass{
public static void main(String args[]){
A a=new C();
if( a instanceof C) // this is true
System.out.println("Yes, a is instanceOf C");
if( a instanceof A) // THIS IS TRUE ?
System.out.println("Yes, a is instanceOf A");
B b=(B) a; // HERE,WHICH OBJECT IS ACTUALLING GETTING CASTED...I THINK C..?
if(b instanceof C) // THIS IS ALSO TRUE
System.out.println("Yes, b is instanceOf C");
b.method();//prints "in C" no problem here

C c=new C();
b=c;
// shouldn't this give me a compiler or runtime error??.NO AS B IS OF TYPE C..SO C IS ASSIGNED TO C

if(b instanceof C)
System.out.println("true");// this prints true why?..THAT IS WHY IT PRINTS TRUE...
}
}

Comments

[Vaneet Bhutani]

Doubt 1: b=c;// shouldn't this give me a compiler or runtime error??
explanation 1: This is a case of automatic conversion. Since C extends B, c is "up the inheritence tree" kind of conversion which is legal.
Doubt 2: if(b instanceof C)
System.out.println("true");// this prints true why?
}
Explanation 2: It returns true b/c b refers to a C object(c)..... thereby b (which is of type C)instanceof C will return true.
Hope it helps,
V