Make code available to other subclasses and subsubclasses

Question

I made a SuperClass (Abstract), a Subclass (Abstract) and a SubSubClass.

There is a piece of code I want to keep in the constructor of the SuperClass, but it won't work correctly unless I put it the Subclass instead.

The SuperClass:

public abstract class SuperClass{

protected int x, y, halfX, halfY;

public SuperClass(){
    halfX = x / 2;
    halfY = y / 2;
}

The SubClass:

public abstract class SubClass extends SuperClass{

public SubClass(int x, int y){
    this.x = x;
    this.y = y;
}

The SubSubClass:

public class SubSubClass extends SubClass{

int half;

public SubSubClass(int x, int y){
    super(x, y);
}

public void myMethod(){
    half = halfX + halfY;
}

If I remove the halfX = x / 2; halfY = y / 2; from the SuperClass constructor and put it into the Subclass constructor, the code works. Like this:

public abstract class SubClass() extends SuperClass{

public SubClass(int x, int y){
    this.x = x;
    this.y = y;

    halfX = x / 2;
    halfY = y / 2;
}
}

I want that piece of code available for other subclasses (and subsubclasses) instead of only in that subclass.

Answer 1

Just as you called super(x, y); in SubSubClass, you need to do the same thing in SubClass. There is no magic to it, just pass the values to the SuperClass so that x and y will be set before you attempt to calculate half the value.

I highly recommend making your fields final where ever possible and in this case they should be final.

BTW: If you want to see what is happening you can step through your code in your debugger.

public abstract class SuperClass{

    protected final int x, y, halfX, halfY;

    public SuperClass(int x, int y){
        this.x = x; // set x before using it.
        this.y = y; // set y before using it.
        halfX = x / 2;
        halfY = y / 2;
    }
}

public abstract class SubClass extends SuperClass{

    private final int z;

    public SubClass(int x, int y, int z){
        super(x, y);
        // only set fields of SubClass
        this.z = z;
    }