public class A {
public void x()
{
System.out.println("A");
}
}
public class B extends A {
public void x()
{
System.out.println("B");
}
}
B b = new B();
A a = (A) b;
a.x();
This code prints "B". Could you tell me why? I thought that it would print "A".
B b is a reference to the new object you created new B()
When you cast the reference from a B to an A, the object is unaltered and untouched and it does exactly the same thing when you call the overridden method x()
Just add this one line in your code and check : System.out.println(a.getClass()); . It prints class B .
B b = new B();
A a = (A) b;
a.x();
System.out.println(a.getClass()); // prints Class B
So basically, even if you cast b to (A), the method being called will be of B. That's polymorphism. Look at the object, provided the reference meets the contract.
Thats because :
This will create a new object of class B with object reference b
B b = new B();
In this u a is the object reference of Class A ,and you are using a=b so it means that a will refer to the same object that b is reffering that is the object of Class B so thats why it goes into the method of Class B and prints B
A a = (A) b;
a.x();
while casting the object, we have following posibilities.. 1.parent=child 2. child=(child)Parent
public class C {
public static void main(String[] args) {
B b = new B(); // b is child
TestPoly t= new TestPoly(); // t is parent
t=(TestPoly)b;//parent=(parent)child i.e parent=child
t.x(); // return B
b=(B)t; //child=(child)parent i.e b=t
b.x(); // return B (because your calling child.x())
B b1 = new B();//child
TestPoly a = (TestPoly) b1;//p=(p)c; ie= p=child
a.x(); //return B
}
}
Bpolymorphismin your headline. Google it and you will find tons of tutorials on that topic.