Common method for the JTextFields to accept only numbers

Question

I limit my JTextFields to accept only numbers. I was using following code for this.

  // my textboxes
  t1=new JTextField(10);
  t2=new JTextField(10);
  t3=new JTextField(10);

  // for the first one
  t1.addKeyListener(new KeyAdapter() {
        public void keyTyped(KeyEvent e) {
          char c = e.getKeyChar();
          if (!((c >= '0') && (c <= '9') ||
             (c == KeyEvent.VK_BACK_SPACE) ||
             (c == KeyEvent.VK_DELETE))) {
            getToolkit().beep();
            e.consume();
          }
        }
      });

Suppose I have 20 texboxes which need the same validation check. So do we need to write this code 20 times? Can I write a common method to implement this? I am new to Swing.

Answer 1

Again, use a DocumentFilter as this will handle copy and paste, this will allow filtering before the Document accepts the text:

import javax.swing.*;
import javax.swing.text.*;

public class DocListenerEg extends JPanel {
   private static final int FIELD_COUNT = 5;
   private JTextField[] fields = new JTextField[FIELD_COUNT];

   public DocListenerEg() {
      MyDocFilter myFilter = new MyDocFilter();
      for (int i = 0; i < fields.length; i++) {
         fields[i] = new JTextField(5);
         ((PlainDocument) fields[i].getDocument()).setDocumentFilter(myFilter);
         add(fields[i]);
      }
   }

   private class MyDocFilter extends DocumentFilter {
      public void insertString(DocumentFilter.FilterBypass fb, int offset,
            String text, AttributeSet attr) throws BadLocationException {
         for (char c : text.toCharArray()) {
            if (!Character.isDigit(c)) {
               return;
            }
         }
         fb.insertString(offset, text.toUpperCase(), attr);
      }

      public void replace(DocumentFilter.FilterBypass fb, int offset,
            int length, String text, AttributeSet attrs)
            throws BadLocationException {
         for (char c : text.toCharArray()) {
            if (!Character.isDigit(c)) {
               return;
            }
         }
         fb.replace(offset, length, text.toUpperCase(), attrs);
      }
   }

   private static void createAndShowGui() {
      DocListenerEg mainPanel = new DocListenerEg();

      JFrame frame = new JFrame("DocListenerEg");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}

Answer 2

Try DocumentFilter as described in http://www.jroller.com/dpmihai/entry/documentfilter

Answer 3

Save your anonymus class into a variable:

KeyListener keyListener= new KeyAdapter() {
    public void keyTyped(KeyEvent e) {
      char c = e.getKeyChar();
      if (!((c >= '0') && (c <= '9') ||
         (c == KeyEvent.VK_BACK_SPACE) ||
         (c == KeyEvent.VK_DELETE))) {
        getToolkit().beep();
        e.consume();
      }
    }
  }

And then

t1.addKeyListener(keyListener);
t2.addKeyListener(keyListener);
t3.addKeyListener(keyListener);
...

Answer 4

Create a class called :

NumberOnlyTextField

Make it extend JTextField, and add the addKeyListener(..) code in the constructor. There you have your very own number validation textfield.

Answer 5

I would make a private boolean method (if it is only used in this class) or public if it it called for elsewhere as well eg. using reg ex:

public boolean checkToBeNumberInput(char c, KeyEvent e){
 if(!char c.matches("[0-9]")||
   (c == KeyEvent.VK_BACK_SPACE) ||
   (c == KeyEvent.VK_DELETE))) {
   getToolkit().beep();
   e.consume();
   return false;

 }
return true;
}

Then call for this boolean method and if it returns true:

if(checkToBeNumberInput()==false){
System.out.println("only numbers are allowed!");
}

This is a fast draft but I hope it helps someone

Answer 6

//look event keypressed . : private void montoingresoKeyPressed(java.awt.event.KeyEvent evt) {

    if(Character.isLetter(evt.getKeyChar()))
    {
        //do what you want on this event, when key is pressed named evt
    }

}