在最终类的构造函数中使用“this”

Question

I have an inner helper class, and I would like to add each new instance of it to a map in the containing class, like this:

public class SomeService {
    private final Map<Integer, ServiceTask> pendingTasksByKey;

    private class ServiceTask {
        private ServiceTask(int key) {
            // initialization...
            pendingTasksByKey.put(key, this);
        }
    }

    // the rest of the code follows
}

When I do it, NetBeans complains about using this in the constructor. OK, I get it, it's a dangerous practice in the general case because someone could extend my class and then I would be leaking this referring to an incompletely initialized object. I didn't want to turn off this warning, so I thought that I could make the class final . This way no one would be able to extend my class, and therefore it should be pretty safe to use this , as the initialization is complete as this point. But NetBeans still shows the warning even if I mark the inner class as final .

Am I right or is there something I missed? Is it just NetBeans being too picky? Besides possible multi-threading memory model issues I can't think of any dangers of such this usage.

Answer 1

It's a Netbeans-specific warning. It is a reminder that the object is not yet constructed so it could be a problem. If you aren't doing anything where that will be a problem then you can ignore it. For example look at this code:

class A {
    public Object obj;

    public A() {
        B b = new B();
        b.addMe(this);

        obj = new Object();
    }
}

class B {
    ArrayList<A> list = new ArrayList<A>(0);

    public void addMe(A a) {
        list.add(a);
        System.out.println(a.obj.toString());
    }
}

This code has a problem and I should not ignore the "leaking this in constructor" warning.

Answer 2

Leaking this in constructor warning has a discussion of this Netbeans warning.

If pendingTasksByKey has a corresponding remove somewhere during the life cycle of these classes I'd say you are right, Netbeans is being picky.