Question

I have 2 textfields in a JFrame and I want to validate the data in textfield1 when the focus gets lost from textfield1. So I have used FocusListener and used showMessageDialog() in the FocusLost() method and that then sets back the focus back to textfield1. It works fine when I click on any component inside the JFrame window other than textfield1,but when I click anywhere outside the JFrame window, the showMessageDialog() gets called two times and the focus goes to textfield2 whereas the focus should remain on textfield1.

    @Override
    public void focusGained(FocusEvent e) {}

    @Override
    public void focusLost(FocusEvent e) {
        boolean show = false;
        String theRegex = "[0-9]";
        Pattern checkRegex = Pattern.compile(theRegex);
        Matcher regexMatcher = checkRegex.matcher( MemberID );
        while ( !regexMatcher.find() && show==false){
            JOptionPane.showMessageDialog(null,"Please enter numbers","Validation Error",JOptionPane.ERROR_MESSAGE);
            MemberID_Text.requestFocusInWindow();
    MemberID_Text.selectAll();
            show = true;

        }

    }

Answer 1

you can do this to verify if a number is entered, and avoid regex all together

     class IntVerifier extends InputVerifier {

  @Override public boolean verify(JComponent input) {
      String text =((JTextField) input).getText();
      int n = 0; 

          try {
      n = Integer.parseInt(text); } 

      catch (NumberFormatException e) {
  return false; 
       }

  return true;
      }
      }

then use the input verifier on the text field

 IntVerifier intv = new IntVerifier();      
 myTextField = new JTextField();
 myTextField.setInputVerifier(intv);