Java Access Abstract Instance variables

Question

I have an abstract class with a variable like follows:

public abstract class MyAbstractClass {

    int myVariable = 1;

    protected abstract void FunctionThatUsesMyVariable();
}

Then when I go to instantiate my class through the following code, myVariable cannot be seen:

MyAbstractClass myClass = new MyAbstractClass() {

    @Override
    protected void FunctionThatUsesMyVariable() {
        // TODO Auto-generated method stub
    }
};

What am I doing wrong and how can I achieve what I am trying to achieve?

dcernahoschi · Accepted Answer · 2013-03-27T10:51:53.067

7

You are declaring myVariable as having package access and your 2 classes reside in different packages. Thus the variable is not visible to inheriting classes. You can declare it with protected access to be visible or put the 2 classes in the same package.

public abstract class MyAbstractClass {

    protected int myVariable = 1;

    protected abstract void FunctionThatUsesMyVariable();
}

edited Mar 27 '13 at 10:51

answered Mar 27 '13 at 10:43

dcernahoschi

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That is only true if the two classes are in different packages. – OldCurmudgeon Mar 27 '13 at 10:50
Thanks, your answer is correct. Just one more question. `myVariable` is a `File` and now it complains about `the local variable may not have been initialized` but the constructor does initialise it? If I did that in a normal class it would not complain, why is it here? – btalb Mar 27 '13 at 12:45
Post the exact the code of the two classes and indicate the line where the compiler complains. But I think it should be another question. – dcernahoschi Mar 27 '13 at 13:45

OldCurmudgeon · Answer 2 · 2013-03-27T10:49:57.840

Seems to work for me:

public class Test {
  public static abstract class MyAbstractClass {
    int myVariable = 1;
    protected abstract void FunctionThatUsesMyVariable();
  }

  public void test() {
    MyAbstractClass myClass = new MyAbstractClass() {
      @Override
      protected void FunctionThatUsesMyVariable() {
        myVariable = 2;
      }
    };
  }

  public static void main(String args[]) {
    new Test().test();
  }
}

I suspect you are declaring the two classes in different packages. If that is what you want then you should make the variable protected (or public if you must). Alternatively - obviously - put them in the same package.

neutrino · Answer 3 · 2013-03-27T10:51:17.180

1

Declare your variable as protected. It's package-private by default.

edited Mar 27 '13 at 10:51

answered Mar 27 '13 at 10:43

neutrino

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score 1 · Answer 4 · answered Mar 27 '13 at 10:43

1

Because you're still subclassing/extending the abstract class and unless you make it protected, the field isn't inherited.

answered Mar 27 '13 at 10:43

Kafkaesque

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Java Access Abstract Instance variables

4 Answers4