Question

Have a look at following scenario:

public class ParentClass {

    private Integer testVar = 1;

    public Integer getTestVar() {
        return testVar;
    }

    public void setTestVar(Integer testVar) {
        this.testVar = testVar;
    }
}


public class ChildClass extends ParentClass {

    private Integer testVar = 2;

    @Override
    public Integer getTestVar() {
        return testVar;
    }

    @Override
    public void setTestVar(Integer testVar) {
        this.testVar = testVar;
    }
}


public class TestClass {

    public static void main(String[] args) {

        ChildClass childClass = new ChildClass();
        childClass.setTestVar(3);
        Gson gson = new Gson();
        String str = gson.toJson(childClass);
        System.out.println(str);
    }
}

Here, I have used com.google.gson.Gson package for json conversion. It gives following output:

{“testVar”: 1}

I expected 3 in the json string, but what I got was the value held by testVar variable of parentClass.

1. Shouldn’t child’s getTestVar over-ride the parent’s counterpart?

2. Is instance member being accessed directly (changing name of instance members of each class, but keeping getters name same proves this)?

3. If yes, how can anyone access private members directly?

EDIT: I’ve edited this question. This version only shows parent’s value in json. Is there a way to get child’s instance member?

Answer 1

1. Yes, it does

2. Yes, Gson accesses fields directly. Other libraries that perform similar tasks often allow you to choose between field and property (i.e. using getters and setters) access, but Gson only supports field access.

3. Private fields are intended to be inaccessible for the regular code, but in some special cases (such as serialization/deserialization) it’s perfectly reasonable to access them directly. That’s why you can access private fields using reflection (see AccessibleObject).