Question

This question is a common issue, and I have tried to look at some thread as Is Java "pass-by-reference" or "pass-by-value"? or How to change an attribute of a public variable from outside the class
but in my case I need to modify a boolean variable, with a Singleton instance.

So far I have a class, and a method which changes the boolean paramter of the class. But I would like to separate this mehod in a manager. The scheme is something like:

public class Test{
    private boolean b;
    public String getb(){}
    public void setb(){}
    String test = ClassSingleton.getInstance().doSomething();
}

public class ClassSingleton{
    public String doSomething(){
        //here I need to change the value of 'b'
        //but it can be called from anyclass so I cant use the set method.
    }
}

Thanks,
David.

Answer 1

If I understand your requirement – this can solve your problem:

public interface IUpdatable
{
    public void setB(boolean newValue);
}

public class Test implements IUpdatable
{
    private boolean b;
    public String getb(){}
    public void setB(boolean newValue) {this.b = newValue;}
}

public class ClassSingleton
{
    public String doSomething(IUpdatable updatable)
    {
        updatable.setB(true);
        ...
    }
}

This way the Singleton does not need to know your Test class – it just knows the interface IUpdatable that supports setting the value of B. Each class that needs to set its B field can implement the interface and the Singleton can update it and remain oblivious to its implementation.