In class hierarchy when a method in subclass has the same name and signature as the method in its super class. Then the method in subclass is said to override method in super class.
when such a overridden method is called through a subclass object then each time subclass version of that method is called. The version of overridden method of super class is hidden.
Ex,
class A
{
int i, j;
A(int a, int b)
{
i = a;
j = b;
}
// display i and j
void show()
{
System.out.println("i and j: " + i + " " + j);
}
}
class B extends A
{
int k;
B(int a, int b, int c)
{
super(a, b);
k = c;
}
// display k -- this overrides show() in A
void show()
{
System.out.println("k: " + k);
}
}
class Override
{
public static void main(String args[])
{
B subOb = new B(1, 2, 3);
subOb.show(); // this calls show() in B
}
}
Why Overridden method?
Overridden method allows supporting runtime polymorphism. It allows a general class to specify methods that will be common to all of its derivatives while allowing subclass to define the specific implementation of some other method.
Dynamic method dispatch (late binding)
Ex,
class A
{
void callme()
{
System.out.println("Inside A's callme method");
}
}
class B extends A
{
// override callme()
void callme()
{
System.out.println("Inside B's callme method");
}
}
class C extends A
{
// override callme()
void callme()
{
System.out.println("Inside C's callme method");
}
}
class Dispatch
{
public static void main(String args[]) {
A a = new A(); // object of type A
B b = new B(); // object of type B
C c = new C(); // object of type C
A r; // obtain a reference of type A
r = a; // r refers to an A object
r.callme(); // calls A's version of callme
r = b; // r refers to a B object
r.callme(); // calls B's version of callme
r = c; // r refers to a C object
r.callme(); // calls C's version of callme
}
}
Posted by:Ruchita Pandya
