why we can't override the variables in java

Question

why we can't override the variables in java , It hides variable

class A {
    int a = 4;
    public void test(){
        System.out.println("Test method of A" );
    }
} 

class B extends A {
    int a = 5;
    public void test(){
        System.out.println("Test method of B" );
    }
    public static void main(String s[]){
        A a= new B();
        System.out.println("Value of a : " a.a );
        System.out.println("Method result " a.test() );
    }
}

Output ::

Value of a : 4
Mthod result :Test method of B

As the B's class test method get called but variable was accessed from super class reference

Already explained [here][1] and [here][2] Regards [1]: http://stackoverflow.com/questions/427756/overriding-a-super-class-instance-variables [2]: http://stackoverflow.com/questions/8983002/how-are-the-variables-overridden-in-java — ultraklon, Feb 06 '13 at 05:57

score 4 · Answer 1 · answered Feb 06 '13 at 05:55

4

It's just how java works. When the code has a B but only 'knows' it has an A, the methods of B will be called but the variables of A will get accessed (since there's no 'method overriding equivalent' for variables). I suggest you wrap variables in getters and setters instead of exposing, so you can control their behaviour in subclasses by overriding the getters and setters.

answered Feb 06 '13 at 05:55

Patashu

21,443
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yes. I want know how java behave in this case – varsha Feb 06 '13 at 05:57

score 0 · Answer 2 · answered Feb 06 '13 at 06:00

0

If you want to access variable of Parent class then use
System.out.println( ((A)a).a );
Type cast the object to its parent and then access it

answered Feb 06 '13 at 06:00

asifsid88

4,631
20
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I think you misunderstood the question. I recommend reading it again. – Paul Bellora Feb 06 '13 at 06:02

score 0 · Answer 3 · answered Feb 06 '13 at 06:14

Assume that you have a method that accepts a parameter of type A

void f(A a) {
     // do something with a.a
}

The writer of the f method has written this method expecting the behavior that is defined by class A. And you want to change this behavior. When you override a method you may or may not change the behavior, and you should not. You can add some other functionality but never change the expected behavior and if you could override a variable you would definitely change the behavior. Check Open/Closed and Liskov Substitution Principles of Object Oriented Design

why we can't override the variables in java

3 Answers3