Re: Constructor

"Mike Schilling" <>
Fri, 26 Sep 2008 12:01:30 -0700
Tom Anderson wrote:

On Fri, 26 Sep 2008, zerg wrote:

Andrea Francia wrote:

public class Main {

  static Foo escaped;

  static class Foo {
    public Foo() {
      escaped = this; // escaping! don't do this at home!
      throw new RuntimeException();

  public static void main(String[] args) {
    try {
      Foo foo = new Foo();
    } catch (RuntimeException e) {
      System.out.println("This reference escaped from constructor:"
+ escaped);

I think you'll find that the above code won't compile. Your IDE or
javac will complain about the use of "this" inside the constructor,
other than for constructor chaining (e.g. "this(args);").

I think you'll find it won't.

Tom and Andrea are (unfortunately) correct.

Note that this kind of escape is a bad idea even if the constructor will
(eventually) succeeed, since it makes a partially constructed object visible
to other threads. NetBeans used to use a pattern like this for its
DataObjects (roughly, objects that represent a file known to the IDE)

    abstract class DataObject
        protected DataObject()
            register(this); // add this to the global list of DataObjects

The result, that other threads in the IDE would now see partially
constructed objects, caused intermittent and intractable problems. I don't
know (and don't at this point really much care) whether this has been fixed.

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