Accessing inherited class variables in java

Question

If you inherit from an activity where certain member variables were declared, how do you access these member variables in the subclass executing the inheritance?

Also check that you don't have a naming conflict: http://java.sys-con.com/node/46344 if you're running into unexpected behavior — jefflunt, Jan 06 '12 at 19:26

score 9 · Accepted Answer · answered Jan 06 '12 at 19:26

public or protected member names can be accessed via this.memberName from any constructor or non-static method or initializer.

private or package level members (accessed from a subclass in a different package) cannot be accessed directly and will need to be accessed via an unprivileged interface such as a public getter.

score 7 · Answer 2 · answered Jan 06 '12 at 19:29

7

class A {
    protected int a = 3;
}

class B extends A {
    protected int b = 2;

    void doIt() {
        System.out.println("super.a:" + super.a);
        System.out.println("this.b: " + this.b);
    }
}

answered Jan 06 '12 at 19:29

ollins

1,851
12
16

1

You don't need the `super` keyword. – mre Jan 06 '12 at 19:29
4

That's right. But this is a beginner question. So, I want to make it absolutely clear. – ollins Jan 06 '12 at 19:33
3

You would only need the `super` keyword if the field was hidden by a field in the subclass. – Ted Hopp Jan 06 '12 at 19:38
1

Also right :) . But I don't want explain the abbreviations. If user1058210 goes this way, everything will be fine... and at some day he will find the shorter solution. – ollins Jan 06 '12 at 19:48

score 3 · Answer 3 · answered Jan 06 '12 at 19:27

If the members were declared private, or if they were declared with default (package) access and your subclass is in a different class, you cannot access the variables. If accessors were provided, you can use those. Otherwise, they are not accessible.

If the members were declared protected or public, then you access them as if they were declared in your own class (this.var, or just var if there's no ambiguity). If you have a member in the subclass with the same name as the superclass, you can use super.var to access the superclass variable.

score 1 · Answer 4 · edited May 23 '17 at 12:00

As stated by others, public and protected fields can be accessed via this.field from the subclass. Package-private fields can also be accessed in the same way, but only if the subclass is in the same package as the parent.

Private fields cannot be accessed in this way, but they can be accessed using Java reflection, if the security settings permit it. It's generally not recommended practice (private members are usually private for a reason), but it can be useful in some situations, for example accessing private class members for code testing purposes. See the answers to this question for how to use reflection in this way.

Accessing inherited class variables in java

4 Answers4