Re: Avoiding NPEs caused by indirect call

Royan <>
Sun, 3 Aug 2008 10:33:52 -0700 (PDT)
On 3 =C1=D7=C7, 19:45, Lew <com.lewscanon@lew> wrote:

Royan wrote:

This is just an example:

public class Model extends AbstractModel {


Your example is incomplete.

Also, you failed to cite (copy and paste) the exception message.

We need more information.

There is a an erroneous cross-post in java.gui, please ignore it

That was not a cross-post, that was a multi-post. =9AA cross-post shows a=


addressed groups in one message. =9AA multi-post shows the same or simila=


message independently as several messages, one per group. =9ACross-postin=

g is

better than multi-posting.

If clj.gui and clj.programmer had different readerships, it would have be=


pointless to tell clj.programmer to ignore clj.gui, wouldn't it?


Hi Lew,

There is not much sense in stack trace, it's classic problem, i'm only
looking for the best solution. If stack really matters here's slightly
improved example that you can even run yourself and stack trace:

package test;

import java.beans.PropertyChangeListener;
import java.beans.PropertyChangeSupport;

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 static void main(String[] args) {
    new Model(new Object());

abstract class AbstractModel {
    public AbstractModel() {

    private void indirectCall() {
    setSomeValue(new Integer(1));

    public void setSomeValue(Integer value) {
        firePropertyChange("someProperty", null, value);

    public void addPropertyChangeListener(PropertyChangeListener
listener) {
    // some code

    protected void firePropertyChange(String propertyName, Object
oldValue, Object newValue) {
        // some code

Exception in thread "main" java.lang.NullPointerException
    at test.Model.firePropertyChange(
    at test.AbstractModel.setSomeValue(
    at test.AbstractModel.indirectCall(
    at test.AbstractModel.<init>(
    at test.Model.<init>(
    at test.Model.main(

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