Very very desperate ....please help!!

Question

I have a very simple but seemingly very hard to solve problem in JBuilder 6 Personal.....
Firstly, I have 2 Application frame, say A frame and B frame, and i have certain JLabel in A frame called HField (which i want to set the field to be hidden). I've link these 2 pages using these statement:
for A frame:
public class A extends JFrame....{
A aFrame;
B bFrame;
public jbinit { // component initialzation
bFrame = new B(this);
void GotoB_actionPerformed(ActionEvent e) {
bFrame.setVisible(true);
this.setVisible(false);
for B frame:
public class B extends JFrame....{
JFrame aFrame;
public B(JFrame tempFrame) {
enableEvents(AWTEvent.WINDOW_EVENT_MASK);
try {
jbinit();
aFrame = tempFrame;
catch {....}
void closeB_actionPerformed(ActionEvent e) {
this.setVisible(false);
aFrame.setVisible(true);
(Some details are omitted.) As a result, the navigation works fine...
Now I'd like B frame to recall HField in A frame to get the data. So i add this statement in both frame:
public A frame.... {
String HField;
HField.setEnabled(false);
public B frame...{
A aFrame;
System.out.println(aFrame.HField);
It's NOT working, and I receive such error:
NullPointerEXception
then i try to create a new class called C, which is just a java class but not application class. I put the variable there and try to recall the variable using:
for B frame:
public B frame...{
C cClass = new C();
System.out.println(cClass.HField);
it works(Surely!!) but when i try to set the variable in A, navigate from A to B and then retrieve it in B , like adding:
for A frame:
public A frame....{
C cClass = new C();
cClass.HField = "ABC";
public B frame...{
C cClass = new C();
System.out.println(cClass.HField);
the NullPinterException comes again.
I have totally NO idea what's happening.... Can anyone help me to solve it out???
Anyone who solves this can get 10 tokens!!! Please help!!!!!!

Answer 1

It's still not working....
I got an error message like
"UserPage.java": Error #: 300 : variable HField not found in class javax.swing.JFrame at line 208, column 30
Well the code for A(indeed Login) frame is like this:
public class Login extends JFrame {
Login login1;
UserPage userPage;
public String HField = "";
public Login() {
enableEvents(AWTEvent.WINDOW_EVENT_MASK);
try {
jbInit();
catch(Exception e) {
e.printStackTrace();
private void jbInit() throws Exception {
userPage = new UserPage(this);
protected void processWindowEvent(WindowEvent e) {
super.processWindowEvent(e);
if (e.getID() == WindowEvent.WINDOW_CLOSING) {
System.exit(0);
void login_actionPerformed(ActionEvent e) {
HField = "YEAH!!!";
this.setVisible(false);
new UserPage().show();
(Of course the login button is initialized)
For B(Indeed UserPage) frame:
public class UserPage extends JFrame {
public JFrame login1;
public UserPage() {
enableEvents(AWTEvent.WINDOW_EVENT_MASK);
try {
jbInit();
catch(Exception e) {
e.printStackTrace();
public UserPage(JFrame aFrame) {
enableEvents(AWTEvent.WINDOW_EVENT_MASK);
try {
jbInit();
login1 = aFrame;
catch(Exception e) {
e.printStackTrace();
private void jbInit() throws Exception {
protected void processWindowEvent(WindowEvent e) {
super.processWindowEvent(e);
if (e.getID() == WindowEvent.WINDOW_CLOSING) {
System.exit(0);
void Back_actionPerformed(ActionEvent e) {
System.out.println(login1.HField);
this.setVisible(false);
new Login().show();
( Back button is initialized also)
So, what's the real problem? I understand virian's thought and try to tackle it but fail to do so......why I cannot create an instance of Login frame and retrieve it in other frame?