Restricting JTextField input to Integers [duplicate]

Solution 1:

Do not use a KeyListener for this as you'll miss much including pasting of text. Also a KeyListener is a very low-level construct and as such, should be avoided in Swing applications.

The solution has been described many times on SO: Use a DocumentFilter. There are several examples of this on this site, some written by me.

For example: using-documentfilter-filterbypass

Also for tutorial help, please look at: Implementing a DocumentFilter.

Edit

For instance:

import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.Document;
import javax.swing.text.DocumentFilter;
import javax.swing.text.PlainDocument;

public class DocFilter {
   public static void main(String[] args) {
      JTextField textField = new JTextField(10);

      JPanel panel = new JPanel();
      panel.add(textField);

      PlainDocument doc = (PlainDocument) textField.getDocument();
      doc.setDocumentFilter(new MyIntFilter());


      JOptionPane.showMessageDialog(null, panel);
   }
}

class MyIntFilter extends DocumentFilter {
   @Override
   public void insertString(FilterBypass fb, int offset, String string,
         AttributeSet attr) throws BadLocationException {

      Document doc = fb.getDocument();
      StringBuilder sb = new StringBuilder();
      sb.append(doc.getText(0, doc.getLength()));
      sb.insert(offset, string);

      if (test(sb.toString())) {
         super.insertString(fb, offset, string, attr);
      } else {
         // warn the user and don't allow the insert
      }
   }

   private boolean test(String text) {
      try {
         Integer.parseInt(text);
         return true;
      } catch (NumberFormatException e) {
         return false;
      }
   }

   @Override
   public void replace(FilterBypass fb, int offset, int length, String text,
         AttributeSet attrs) throws BadLocationException {

      Document doc = fb.getDocument();
      StringBuilder sb = new StringBuilder();
      sb.append(doc.getText(0, doc.getLength()));
      sb.replace(offset, offset + length, text);

      if (test(sb.toString())) {
         super.replace(fb, offset, length, text, attrs);
      } else {
         // warn the user and don't allow the insert
      }

   }

   @Override
   public void remove(FilterBypass fb, int offset, int length)
         throws BadLocationException {
      Document doc = fb.getDocument();
      StringBuilder sb = new StringBuilder();
      sb.append(doc.getText(0, doc.getLength()));
      sb.delete(offset, offset + length);

      if (test(sb.toString())) {
         super.remove(fb, offset, length);
      } else {
         // warn the user and don't allow the insert
      }

   }
}

Why is this important?

• What if the user uses copy and paste to insert data into the text component? A KeyListener can miss this?
• You appear to be desiring to check that the data can represent an int. What if they enter numeric data that doesn't fit?
• What if you want to allow the user to later enter double data? In scientific notation?

Solution 2:

You can also use JFormattedTextField, which is much simpler to use. Example:

public static void main(String[] args) {
    NumberFormat format = NumberFormat.getInstance();
    NumberFormatter formatter = new NumberFormatter(format);
    formatter.setValueClass(Integer.class);
    formatter.setMinimum(0);
    formatter.setMaximum(Integer.MAX_VALUE);
    formatter.setAllowsInvalid(false);
    // If you want the value to be committed on each keystroke instead of focus lost
    formatter.setCommitsOnValidEdit(true);
    JFormattedTextField field = new JFormattedTextField(formatter);

    JOptionPane.showMessageDialog(null, field);

    // getValue() always returns something valid
    System.out.println(field.getValue());
}

Solution 3:

I can't believe I haven't found this simple solution anywhere on stack overflow yet, it is by far the most useful. Changing the Document or DocumentFilter does not work for JFormattedTextField. Peter Tseng's answer comes very close.

NumberFormat longFormat = NumberFormat.getIntegerInstance();

NumberFormatter numberFormatter = new NumberFormatter(longFormat);
numberFormatter.setValueClass(Long.class); //optional, ensures you will always get a long value
numberFormatter.setAllowsInvalid(false); //this is the key!!
numberFormatter.setMinimum(0l); //Optional

JFormattedTextField field = new JFormattedTextField(numberFormatter);

Solution 4:

Here's one approach that uses a keylistener,but uses the keyChar (instead of the keyCode):

http://edenti.deis.unibo.it/utils/Java-tips/Validating%20numerical%20input%20in%20a%20JTextField.txt

 keyText.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();
      }
    }
  });

Another approach (which personally I find almost as over-complicated as Swing's JTree model) is to use Formatted Text Fields:

http://docs.oracle.com/javase/tutorial/uiswing/components/formattedtextfield.html