Java superclass field initialised in subclasses

Question

I have a Java superclass with a private field 'variable' and all its subclasses use 'variable' the same way. Except in every subclass 'variable' gets calculated differently upon initialisation. Where do I best store this field and how do I best initialise it?

This is my code:

public abstract class SuperClass {

    private int variable;

    public abstract String getName();

    public void printVariable() { System.out.println(variable); }

    public int squareVariable() { 
        variable *= variable; 
        return variable;
    }

}

public class SubClass1 extends SuperClass {

    private String name;

    public SubClass1(int param) {
        name = "SubClass1";

        super.variable = param + 1;
        // How do I make this better?
    }

    public String getName() { return name; }

}

public class SubClass2 extends SuperClass {

    private String name;

    public SubClass2(int param) {
        name = "SubClass2";

        super.variable = param / 2;
        // How do I make this better?
    }

    public String getName() { return name; }

}

As you can see, right now I use super.variable, but then I have to make 'variable' protected and that approach doesn't seem optimal to me. What is the right way to do this? Should I define a setter in the superclass? Or can I define a constructor in the superclass which handels this? Or should I store 'variable' in each subclass separately? Or should I keep it like this and make 'variable' protected?

Answer 1

First, the code in the question doesn't compile ( The field SuperClass.variable is not visible ), so they are bad examples to being with.

Store both variable and name in SuperClass , and initialize them in a constructor.

public abstract class SuperClass {

    private String name;
    private int variable;

    protected SuperClass(String name, int variable) {
        this.name = name;
        this.variable = variable;
    }

    public String getName() { return name; }

    public void printVariable() { System.out.println(variable); }

    public int squareVariable() { 
        variable *= variable; 
        return variable;
    }

}

public class SubClass1 extends SuperClass {

    public SubClass1(int param) {
        super("SubClass1", param + 1);
    }

}

public class SubClass2 extends SuperClass {

    public SubClass2(int param) {
        super("SubClass2", param / 2);
    }

}