Variable inheritance in Java (Beginner)

Question

I have a class A with a variable bool var = true and a getter method getVar(). I'm trying to create a class B that extends A and redefines var to bool var = false. The code:

public class A{
    protected boolean var = true;
    public boolean getVar(){
        return var;
    }
}

public class B extends A{
    protected boolean var = false;
}

The problem is that if I execute:

B b_class = new B();
System.out.println(b_class.getVar());

I obtain true and I don't undestand why. What I'm doing wrong?

You can't do B.getVar(), since the method isn't static. I assume you mean b_class.getVar() and fixed it. — kba
– kba, Commented Jan 15, 2012 at 18:47

Sean Owen · Accepted Answer · 2012-01-15 18:39:51Z

7

You don't "inherit" variables; B.var merely hides A.var, but only in B. You are calling getVar(), a method in A, which sees A.var, which is true.

answered Jan 15, 2012 at 18:39

Sean Owen

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Comments

Ted Hopp · Accepted Answer · 2012-01-15 18:40:12Z

3

You are declaring a new var field in B that is hiding A.var. Try this instead:

public class B extends A {
    public B() {
        var = false;
    }
}

answered Jan 15, 2012 at 18:40

Ted Hopp

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Comments

Codemwnci · Accepted Answer · 2012-01-15 18:46:28Z

2

You shouldn't be creating a new instance variable in your overridden class, because it can't be seen by the super class (A), and therefore when getVar() is called, it will return the value it can see. You should instead be setting the value of var in the constructor to be what you want.

public B() {
    var = false;
}

edited Jan 15, 2012 at 18:46

answered Jan 15, 2012 at 18:40

Codemwnci

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Comments

A. Randhawa · Accepted Answer · 2015-11-09 08:09:42Z

1

Variable initialized in the super class can’t be changed like this. You have already declared protected boolean var = true. So, no matter what you do in extended class it will always show you true.

answered Nov 9, 2015 at 8:09

A. Randhawa

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Comments

OnResolve · Accepted Answer · 2012-01-15 18:40:40Z

0

GetVar isn't defined in B so polymorphism jumps to A where var is true.

answered Jan 15, 2012 at 18:40

OnResolve

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