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Null pointer exception while getting other applet in the same page

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Join Date: May 2008
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dayanandabv dayanandabv is offline Offline
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Null pointer exception while getting other applet in the same page

 
0
  #1
May 6th, 2008
Hi all,
I am getting Null pointer exception while getting other applet in the same page, can guide what i am doing wrong

here is demo code
Java Syntax (Toggle Plain Text) 
  1. // First applet
  2.  
  3. import java.applet.Applet;
  4. public class Applet1 extends javax.swing.JApplet {
  5.  
  6.     Applet applet1 = null;
  7.     public void init() {
  8.         try {
  9.             java.awt.EventQueue.invokeAndWait(new Runnable() {
  10.                 public void run() {
  11.                     initComponents();
  12.                 }
  13.             });
  14.         } catch (Exception ex) {
  15.             ex.printStackTrace();
  16.         }
  17.  
  18.         applet1 = getAppletContext().getApplet("App2");
  19.         System.out.println("Oh at last i found"+applet1);
  20.  
  21. //        Enumeration allAppletsOnSamePage = getAppletContext().getApplets();
  22. //        while(allAppletsOnSamePage.hasMoreElements()) {
  23. //            System.out.println("Ohhhhhhh-- "+allAppletsOnSamePage.nextElement().toString());
  24. //        }
  25.     }
  26.     // <editor-fold defaultstate="collapsed" desc=" Generated Code ">                          
  27.     private void initComponents() {
  28.         jButton1 = new javax.swing.JButton();
  29.         jLabel1 = new javax.swing.JLabel();
  30.  
  31.         jButton1.setText("hi");
  32.         jButton1.addActionListener(new java.awt.event.ActionListener() {
  33.             public void actionPerformed(java.awt.event.ActionEvent evt) {
  34.                 jButton1ActionPerformed(evt);
  35.             }
  36.         });
  37.  
  38.         jLabel1.setText("jLabel1");
  39.  
  40.         javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
  41.         getContentPane().setLayout(layout);
  42.         layout.setHorizontalGroup(
  43.             layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
  44.             .addGroup(layout.createSequentialGroup()
  45.                 .addGap(111, 111, 111)
  46.                 .addComponent(jButton1)
  47.                 .addContainerGap(248, Short.MAX_VALUE))
  48.             .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
  49.                 .addContainerGap(187, Short.MAX_VALUE)
  50.                 .addComponent(jLabel1)
  51.                 .addGap(179, 179, 179))
  52.         );
  53.         layout.setVerticalGroup(
  54.             layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
  55.             .addGroup(layout.createSequentialGroup()
  56.                 .addGap(67, 67, 67)
  57.                 .addComponent(jButton1)
  58.                 .addGap(29, 29, 29)
  59.                 .addComponent(jLabel1)
  60.                 .addContainerGap(94, Short.MAX_VALUE))
  61.         );
  62.     }// </editor-fold>                        
  63.  
  64.     private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
  65.         if(applet1!=null){
  66.             ((Applet2)applet1).setTextLabel("How are you");
  67.         }
  68.     }                                        
  69.  
  70.  
  71.     // Variables declaration - do not modify                     
  72.     private javax.swing.JButton jButton1;
  73.     private javax.swing.JLabel jLabel1;
  74.     // End of variables declaration                   
  75.  
  76. }
  77.  
  78.  
  79. // Second applet
  80. import java.applet.Applet;
  81.  
  82. /**
  83.  *
  84.  * @author  dayananda.bv
  85.  */
  86. class Applet2 extends javax.swing.JApplet {
  87.  
  88.     /** Initializes the applet Applet1 */
  89.     public void init() {
  90.         try {
  91.             java.awt.EventQueue.invokeAndWait(new Runnable() {
  92.                 public void run() {
  93.                     initComponents();
  94.                 }
  95.             });
  96.         } catch (Exception ex) {
  97.             ex.printStackTrace();
  98.         }
  99.     }
  100.  
  101.     public void setTextLabel(String text){
  102.         jLabel1.setText(text);
  103.     }
  104.     /** This method is called from within the init() method to
  105.      * initialize the form.
  106.      * WARNING: Do NOT modify this code. The content of this method is
  107.      * always regenerated by the Form Editor.
  108.      */
  109.     // <editor-fold defaultstate="collapsed" desc=" Generated Code ">                          
  110.     private void initComponents() {
  111.         jLabel1 = new javax.swing.JLabel();
  112.  
  113.         jLabel1.setText("HI");
  114.  
  115.         javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
  116.         getContentPane().setLayout(layout);
  117.         layout.setHorizontalGroup(
  118.             layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
  119.             .addGroup(layout.createSequentialGroup()
  120.                 .addGap(80, 80, 80)
  121.                 .addComponent(jLabel1, javax.swing.GroupLayout.PREFERRED_SIZE, 135, javax.swing.GroupLayout.PREFERRED_SIZE)
  122.                 .addContainerGap(185, Short.MAX_VALUE))
  123.         );
  124.         layout.setVerticalGroup(
  125.             layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
  126.             .addGroup(layout.createSequentialGroup()
  127.                 .addGap(45, 45, 45)
  128.                 .addComponent(jLabel1)
  129.                 .addContainerGap(113, Short.MAX_VALUE))
  130.         );
  131.     }// </editor-fold>                        
  132.  
  133.  
  134.     // Variables declaration - do not modify                     
  135.     private javax.swing.JLabel jLabel1;
  136.     // End of variables declaration                   
  137.  
  138. }
Java Syntax (Toggle Plain Text) 
  1. //html code
  2. <HTML>
  3. <HEAD>
  4.    <TITLE>Applet HTML Page</TITLE>
  5. </HEAD>
  6. <BODY>
  7. <P>
  8. <APPLET NAME="App1" codebase="classes" code="Applet1.class" width=350 height=200></APPLET>
  9. </P>
  10.  
  11. <P>
  12. <APPLET NAME="App2" codebase="classes" code="Applet2.class" width=350 height=200></APPLET>
  13. </P>
  14. </BODY>
  15. </HTML>
Last edited by dayanandabv; May 6th, 2008 at 7:32 am.
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Re: Null pointer exception while getting other applet in the same page

 
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  #2
May 6th, 2008
At which line do you get the Exception? What does the console prints. Try adding try-catch with printstacktrace so you can provide us with more information
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Re: Null pointer exception while getting other applet in the same page

 
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  #3
May 6th, 2008
hi, thanks for quick replay.

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Originally Posted by javaAddict View Post
At which line do you get the Exception? What does the console prints. Try adding try-catch with printstacktrace so you can provide us with more information
when i am getting applet2 object in the beging of the init method in Applet1, hope the Applet1 is loading first after that Applet2 is loading so that i am getting null pointer exception.

Java Syntax (Toggle Plain Text) 
  1.    applet2 = getAppletContext().getApplet("App2");
can you tell me how can wait until the seconde applet(Applet2) should load after that only i need to load applet1.
hope you understood.

Thanks
Dayananda BV
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