CODEWITHSUNDEEP
javaprivate
ralphxiaoz
ralphxiaoz

Reputation: 101

JAVA inheritance access

I'm currently learning JAVA and got confused on the access in inheritance. The case below:

public class Father{
    private int age;

    public void setAge(int a){
        age = a;
    }

    public void getAge(){
        System.out.println(age);
    }
} //End of Father

public class Son extends Father{

} //End of Son

public class Test{
    public static void main(String[] args) {
        Father F = new Father();
        Son S = new Son();

        F.setAge(40);
        F.getAge();

        S.setAge(20);
        S.getAge();

        //System.out.println(F.age);
    }
} //End of Test

In the case above, "age" is a private variable in Father. Although Son extends Father, this private variable "age" is not inherited. Which means there is no variable in Son.

But when I put them into Test, running result shows "40" and "20", as if there was an int variable in Son. How to explain this?

Upvotes: 0

Views: 86

Answers (4)

David H. Bennett
David H. Bennett

Reputation: 1842

Your setters and getters are public so they are exposed in to the sub-class Son. The code for the setter and getter is contained in the super-class Father which has access to the private field 'age' in that class definition.

If you were to change the setter and getter to private then the sub-class Son would not have access to age field in the super-class Father.

public class Father{
    // only this class may access the field directly
    private int age;

    // this class,sub-classes and package classes may set the age
    protected void setAge(int a){
        age = a;
    }

    // you can get the age from anywhere
    public void getAge(){
        System.out.println(age);
    }
} //End of Father

Upvotes: 0

Warren Dew
Warren Dew

Reputation: 8938

Private variables are still there in subclasses; they are just not visible to the subclass. Since the getAge() method is public in the superclass, and thus in the subclass, you can still invoke it to cause the private variable to be printed.

Upvotes: 0

Bathsheba
Bathsheba

Reputation: 234875

age is inherited. It's just that you can't access it directly from son.

If you want to access it directly in son then mark it as protected and not private, i.e. declare

 protected int age;

in the Father class.

(By the way, the normal thing to do would be to have getAge() return an int, and your calling function write the age to the console).

Upvotes: 2

La-comadreja
La-comadreja

Reputation: 5755

setAge() and getAge() are the public methods and the instance variable is being accessed through those methods, which are directly inherited. The instance variable is not being accessed directly, i.e. by direct manipulation outside methods in the class Father.

Upvotes: 0

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