FULL PRODUCT VERSION :


A DESCRIPTION OF THE PROBLEM :
import java.awt.*;

/** NoisyFlowLayout.java

Demonstrates a bug in Container.addImpl() in which
LayoutManagers which do not implement LayoutManager2
are not notified when a Component is added unless both
a contstraint/name is provided and it is not null.

Expected output:
  adding java.awt.Label[...,text=1] at null
  adding java.awt.Label[...,text=2] at non-null
  adding java.awt.Label[...,text=3] at null
  adding java.awt.Label[...,text=4] at non-null
  adding java.awt.Label[...,text=5] at null

Actual output:
  adding java.awt.Label[...,text=2] at non-null
  adding java.awt.Label[...,text=4] at non-null

The problem is that Container.addImpl() does this:

  if (layoutMgr != null) {
    if (layoutMgr instanceof LayoutManager2) {
        ((LayoutManager2)layoutMgr).addLayoutComponent(comp, constraints);
    } else if (constraints instanceof String) {
        layoutMgr.addLayoutComponent((String)constraints, comp);
    }
  }

when it should be doing this:

  if (layoutMgr != null) {
    if (layoutMgr instanceof LayoutManager2) {
        ((LayoutManager2)layoutMgr).addLayoutComponent(comp, constraints);
    } else {
        layoutMgr.addLayoutComponent((constraints instanceof String)?(String)constraints:null, comp);
    }
  }

I think this is a bug. But if somehow this is declared "not a bug"
then at the very least this behaviour should be documented. (You
will definitely have to mention that while a LayoutManager2 will
have addLayoutComponent() called every time a component is added
to the Container, that a plain LayoutManager will only have
addLayoutComponent() called when a non-null constraint is provided.)

Also see bug#4413418 which indirectly reported this problem, but
then got it wrong in the Evaluation and dismissed it.
*/
public class NoisyFlowLayout extends FlowLayout {

  public void addLayoutComponent(String name, Component comp) {
    System.out.println("adding " + comp + " at " + name);
    super.addLayoutComponent(name, comp);
  }

  public static void main(String[] argv) {
    String constraint = "non-null", nullConstraint = null;
    Panel p = new Panel(new NoisyFlowLayout());
    p.add(new Label("1"));
    p.add(new Label("2"), constraint);
    p.add(new Label("3"), nullConstraint);
    p.add(constraint, new Label("4"));
    p.add(nullConstraint, new Label("5"));
  }
}



REPRODUCIBILITY :
This bug can be reproduced always.