NPE with JTextArea

[scott beveridge]

Hi,

I get an NullPointerException when I try and call a append() or setText() method for a JTextArea but not a JTextField when everything else remains the same. Here is the revelant code.

import javax.swing.*;
import javax.swing.border.*;
import java.awt.*;
import java.awt.event.*;
 
public class SHIP extends JFrame
 
private JTextField outputJTextField,
private TextArea auditJTextArea;
 
   public SHIP()
   {
      createUserInterface();
   }
   
   // create and position GUI components
   private void createUserInterface()
 {
//set up outputJTextField
      outputJTextField = new JTextField();
      outputJTextField.setBounds( 40, 80, 600, 20);
      outputJTextField.setEditable ( false );
      contentPane.add ( outputJTextField );
 
  //set up auditJTextArea
      JTextArea auditJTextArea= new JTextArea();
      auditJTextArea.setBounds( 8, 150, 630,160);
      auditJTextArea.setEditable ( false );
      contentPane.add ( auditJTextArea );
 
      }// end create GUI method
 
 
    //method to set output text
      public void guisetoutput(String output ){
      outputJTextField.setText ( output );}
    
    //method to append JTextArea text
    public void addaudit(String audit ){
    auditJTextArea.append( audit );}
    
    

Then from another class file.

 
 SHIP app = new SHIP();
 
 app.guisetoutput( "Hello");
    app.addaudit( "Hello" );
 

As I said setting the JTextField works fine, but I get an NPE pointing at both references to the JTextArea, please someone tell me what I've done wrong. I'm using JCreator and XP.

Thanks,

Scott

[ June 11, 2005: Message edited by: scott beveridge ]
[ June 11, 2005: Message edited by: scott beveridge ]

[KR Campbell]

Your problem is that you have two variables with the same name but different scope. You have instantiated the local version in createUserInterface() but not the instance variable. Thus, the local one hides the other one. Try:

auditJTextArea= new JTextArea(); 

instead of:

 JTextArea auditJTextArea= new JTextArea(); 

Regards
Kenny

[KR Campbell]

... that is, it hides it within the scope of the method.

[scott beveridge]

Thanks for the reply. This still does not work.

I originally had this but changed it because:
When I try this now I get a compile error of

"cannot resolve symbol:
auditJTextArea = new JTextArea();"

and of course everywhere that references it.

I've retyped "new JTextArea()" a thousand times but still no joy.

Scott

[Ernest Friedman-Hill]

I don't know about "can't resolve symbol" errors, but you ought to get an "invalid type" error, because auditJTextArea is declared as a TextArea, but you're assigning a JTextArea to it -- those are two different classes.

[Abdulla Mamuwala]

Looking back at what Earnest said,

 private TextArea auditJTextArea 

Here auditJTextArea has a reference type TextArea.

auditJTextArea = new JTextArea()  

and here the runtime object for auditJTextArea is of type auditJTextArea.

Both TextArea and auditJTextArea belong to different class hierarchies, this gives a "Type Mismatch" compile time error.

[scott beveridge]

Yeah I've tried both TextArea and JTextArea, usually not at the same time (that doesn't work either).

I think the problem is a mistake in scope somewhere.
I'll keep trying and thanks for your input.

scott