Update fields from superclass

Question

From point of various patterns is it acceptable to change fields in superclass from its descendants. For example:

class A {
    int barA;
}

class B extends A {
    private void testMethod() {
        barA = 4;
    }
}

Thanks in advance!

Answer 1

No, it's generally not a good idea. If I understand what you are asking, it would normally be done like

public class A{
     private int val;

     protected void setVal(int i){
        val = i;
     }

     public int getVal(){
        return val;
     }
}

public class B extends A{
    public void test(){
        this.setVal(4);
    }
} 

Answer 2

It is generally a better practice to make all your fields private, and provide public or protected setters if you want to change their value in subclasses.

Answer 3

Yes, this is fine. If the superclass doesn't want subclasses modifying values, it can make them private.

Answer 4

When we say class B extends A, we mean that it inherits all its (superclass' i.e. A's) variables as well. So now B has its own variable barA. Thus you can change it just like any other member variable. Further read this.

Answer 5

It is ok to do that but instead why don't you create a getter/setter for the same ? It is much better to use those instead of modifying directly.

If you do not want the values modified in the subclass, make them final.