Avoiding NPEs caused by indirect call

Royan <romayankin@gmail.com>
Sun, 3 Aug 2008 08:26:06 -0700 (PDT)
This is just an example:

public class Model extends AbstractModel {
    private final PropertyChangeSupport propertyChangeSupport;

    public Model (Object source) {
        propertyChangeSupport = new PropertyChangeSupport(source);

    public void addPropertyChangeListener(PropertyChangeListener
listener) {

    public void firePropertyChange(String propertyName, Object
oldValue, Object newValue) {
oldValue, newValue);

public abstract class AbstractModel {
    public void setSomeValue(Value value) {
        firePropertyChange("someProperty", oldValue, value);

Imagine that I want to introduce PropertyChangeSupport to my custom
class. I'm bound to provide source for the event in a
PropertyChangeSupport constructor at the same time I'm getting
NullPointerException in Model#firePropertyChange() every time
AbstractModel#setSomeValue(Value) is called before Model object has
been constructed

OK There are a few ways of rectifying the problem, but none of them
appear to me as a good solution. I could override setSomeValue method,
but I do need its functionality and don't want to replicate it.

I could add validation: if(propertyChangeSupport == null)
{super.firePropertyChange(...)} but this is also kind of a hack which
I don't really like.

What would be your advice?

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