Leaking this in constructor warning

Question

I'd like to avoid (most of the) warnings of Netbeans 6.9.1, and I have a problem with the 'Leaking this in constructor' warning.

I understand the problem, calling a method in the constructor and passing "this" is dangerous, since "this" may not have been fully initialized.

It was easy to fix the warning in my singleton classes, because the constructor is private and only called from the same class.

Old code (simplified):

private Singleton() {
  ...
  addWindowFocusListener(this);
}

public static Singleton getInstance() {

  ...
  instance = new Singleton();
  ...
}

New code (simplified):

private Singleton() {
  ...
}

public static Singleton getInstance() {

  ...
  instance = new Singleton();
  addWindowFocusListener( instance );
  ...
}

This fix is not working if the constructor is public and can be called from other classes. How is it possible to fix the following code:

public class MyClass {

  ...
  List<MyClass> instances = new ArrayList<MyClass>();
  ...

  public MyClass() {
    ...
    instances.add(this);
  }

}

Of course I want a fix which does not require to modify all my codes using this class ( by calling an init method for instance).

Answer 1

Since you make sure to put your instances.add(this) at the end of the constructor you should IMHO be safe to tell the compiler to simply suppress the warning (*). A warning, by its nature, doesn't necessarily mean that there's something wrong, it just requires your attention.

If you know what you're doing you can use a @SuppressWarnings annotation. Like Terrel mentioned in his comments, the following annotation does it as of NetBeans 6.9.1:

@SuppressWarnings("LeakingThisInConstructor")

(*) Update: As Isthar and Sergey pointed out there are cases where "leaking" constructor code can look perfectly safe (as in your question) and yet it is not. Are there more readers that can approve this? I am considering deleting this answer for the mentioned reasons.