Subtyping

In java, its a feature, where an object of subclass be assigned to an object of its superclass.

Number myNumber = new Number();
Long telephoneNo = new Long(27000134);
myNumber = telephoneNo;

Similarly in the case of method calls, a sub-class object can be passed as a parameter to a method, that is has a super-class object as a parameter in its defination.

public void someMethod(Number n){
   ......
}

someMethod(new Integer(10));
someMethod(new Double(10.1));

The above feature can also be implemented using generics as follows:

Box box = new Box();
box.add(new Integer(10));
box.add(new Double(10.1));

tutorials