15.11.4

Runtime Evaluation of Method Invocation

EXPRESSIONS

15.11.4.10

Example: Method Invocation using

super

An overridden instance method of a superclass may be accessed by using the key 

word

super

 to access the members of the immediate superclass, bypassing any

overriding declaration in the class that contains the method invocation.

When accessing an instance variable,

super

 means the same as a cast of

this

( 15.10.2), but this equivalence does not hold true for method invocation. This is

demonstrated by the example:

class T1 {

String s() { return "1"; }

}

class T2 extends T1 {

String s() { return "2"; }

}

class T3 extends T2 {

String s() { return "3"; }

void test() {

System.out.println("s()=\t\t"+s());

System.out.println("super.s()=\t"+super.s());

System.out.print("((T2)this).s()=\t");

System.out.println(((T2)this).s());

System.out.print("((T1)this).s()=\t");

System.out.println(((T1)this).s());

}

}

class Test {

public static void main(String[] args) {

T3 t3 = new T3();

t3.test();

}

}

which produces the output:

s()=

3

super.s()=

2

((T2)this).s()= 3

((T1)this).s()= 3

The casts to types

T1

 and

T2

 do not change the method that is invoked, because

the instance method to be invoked is chosen according to the run time class of the

object referred to be

this

. A cast does not change the class of an object; it only

checks that the class is compatible with the specified type.

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