i have a feild where the user must insert only integer values not chars..if they insert a char an error messege should appear..how can i do this and what is the code to do it

You can test this using a loop which goes through the numbers: "0123456789" If this condition is valid then proceed to the next part of the program. For this you can use a key listener.

actually how do i write the code..i dont know anything abt keylister i am a newbie for java
can u give me a sample code

actually how do i write the code..i dont know anything abt keylister i am a newbie for java
can u give me a sample code

Something like this?

KeyView.java

import javax.swing.*; 
  import java.awt.event.*; 
 import java.awt.*; 
  
  class KeyView extends JFrame implements KeyListener { 
     JTextField keyText = new JTextField(80); 
     JLabel keyLabel = new JLabel("Type in a number mo fo."); 
 
     KeyView() { 
         super("KeyView"); 
         setSize(350, 100); 
         setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
         keyText.addKeyListener(this); 
         Container pane = getContentPane(); 
         BorderLayout bord = new BorderLayout(); 
         pane.add(keyLabel, BorderLayout.NORTH); 
         pane.add(keyText, BorderLayout.CENTER); 
         setContentPane(pane); 
         setVisible(true); 
     } 
 
     public void keyTyped(KeyEvent input) { 
         char key = input.getKeyChar();
         if (key >='0'&& key <='9')
         {
            keyLabel.setText("You pressed " + key); 
         }
         else
             keyLabel.setText("I said press a freaking number?");
     } 
 
     public void keyPressed(KeyEvent txt) { 
         // do nothing 
     } 
 
     public void keyReleased(KeyEvent txt) { 
         // do nothing 
     } 
 
    public static void main(String[] arguments) { 
        
         try {
       UIManager.setLookAndFeel(
           "com.sun.java.swing.plaf.windows.WindowsLookAndFeel" );


      } catch (Exception e) { }

     new KeyView(); 
     } 
 }

Or you could wait till the user enters the entire expression and parse it at the end?

KeyListener will do what exactly what you wanna do.

hai, check this code and hope this helps u.

/*in ur main program where u have ur textfield, declare the TextField as follows*/

JTextField txtInput =username = new JTextField(new FixedNumericDocument(4,true),"",15);

/*where 4 is the maximum number of digits that is allowed, boolean true denotes whether u need the text box to accept only integers and false otherwise, and 15 is the size of the text field.*/

/* Then as a seperate class call the following code*/

///////FixedNumericDocument.java////////
import javax.swing.*;
import javax.swing.text.*;
import java.awt.*;
public class FixedNumericDocument extends PlainDocument {
private int maxLength = 9999;
private boolean numericOnly;
public FixedNumericDocument(int maxLength, boolean numericOnly) {
super();
this.maxLength = maxLength;
this.numericOnly = numericOnly;
}
//this is where we'll control all input to our document.
//If the text that is being entered passes our criteria, then we'll just call
//super.insertString(...)
public void insertString(int offset, String str, AttributeSet attr) throws BadLocationException {
if (getLength() + str.length() > maxLength) {
Toolkit.getDefaultToolkit().beep();
return;
}
else {
try {
if (numericOnly) {
//check if str is numeric only
Integer.parseInt(str);
//if we get here then str contains only numbers
//so it's ok to insert
}
super.insertString(offset, str, attr);
}
catch(NumberFormatException exp) {
Toolkit.getDefaultToolkit().beep();
return;
}
}
return;
}
}