How to change a variable from a method

This question is a common issue, and I have tried to look at some thread as Is Java "pass-by-reference&qu开发者_如何学编程ot; 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.

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.

1. You could extract public void setb(){} into an interface (let's call it BSettable), make Test implement BSettable, and pass an argument of type BSettable into doSomething.

2. Alternatively, you could make b into an AtomicBoolean and make doSomething accept (a reference to) an AtomicBoolean.

Define b as static variable.

Then call Test.b = value

Perhaps:

public class Test {
   private static boolean b;
   public static String getB() {}
   public static void setB() {}
}

should help? Static fields and methods can be called without an instance (i.e. Test.setB();).

I think your question is not very clear and your sample code is really badly done. Do you actually mean something like this?

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

public class ClassSingleton{
    private static ClassSingleton __t__ = new ClassSingleton();
    private ClassSingleton() {} 
    public String doSomething(Test t){
        t.setb(true);
        return null;
    }

    public static ClassSingleton getInstance(){
        return __t__;
    }
}

Do you mean your manager is a singleton? or your test class should be singleton? Please be more specific