Question

For instance,

public Foo{
    private Object mutex = new Object();
    private int bar;

    public Foo(Foo f){
        this.mutex = f.getMutex();
        this.bar = f.getBar();
    }

    public Object getMutex(){
        return mutex;
    }

    public void setBar(int bar){
        synchronized(mutex){
            this.bar = bar;
        }
    }

    public int getBar(){
        synchronized(mutex){
            return bar;
        }
    }
}

Answer 1

It depends – do you want the two objects to share a mutex (a shallow copy, really) or do you want them to be independent? In most cases I’d expect the latter, in which case you wouldn’t want to copy the reference.