Overridable Method Calls From the Constructor

PMD and NetBeans both give warnings about calling non-final non-private methods from the constructor of a class.

I never really understood why it was such a bad thing until today. I was hit by the problem it causes when subclassing one of the swing model classes.

public class CustomButtonModel extends DefaultButtonModel {
    private final SomeClass object;
    public CustomButtonModel(SomeClass object) {
        if (object == null)
            throw new IllegalArgumentException("null object is a nono");
            this.object = object;
        }
        public void setEnabled(boolean enabled) {
            super.setEnabled(enabled && object.evaluate());
        }
    }
}

And i was getting a NullPointerException in setEnabled which should be impossible if you just look at the class. Running a debugger I could confirm that object was null but it took quite a while to figure out that DefaultButtonModel was calling setEnabled() from its default constructor before object had been assigned.