Check user has entered the correct number of symbols in a text field

Question

I have small Java GUI program (screenshot below). One of the values is "Passport Number".

This field should contain 11 symbols. Once the user has entered a value in this field, I want to check the correct number of symbols are in place and set string "error" in Label item "Label1" if not.

I tried this:

private void btnSendActionPerformed(java.awt.event.ActionEvent evt) { 
   String error;                                       
   if(passportn.length()!=11) {
     error="error";
     label1.setText(error);
   }
 }

This works but only when a button is pressed. Instead I want this to happen as the user enters passport number.

screenshot

I think you can find your answer at a similar post http://stackoverflow.com/questions/3953208/value-change-listener-to-jtextfield — Orel Eraki, Dec 05 '13 at 11:04

score 2 · Accepted Answer · answered Dec 05 '13 at 11:22

1) You can use InputVerifier like next :

final JLabel l = new JLabel(" ");
JTextField field = new JTextField();
field.setInputVerifier(new InputVerifier() {

    @Override
    public boolean verify(JComponent arg0) {
        Boolean b = ((JTextField)arg0).getText().length() == 11;
        if(!b){
            l.setText("error");
        } else {
            l.setText("accepted");
        }
        return b;
    }
});

with that before you enter 11 characters you cant to set focus to another component.

2) Use DocumentListener, for example :

final JLabel l = new JLabel(" ");

JTextField field = new JTextField();
field.getDocument().addDocumentListener(new DocumentListener() {

    @Override
    public void removeUpdate(DocumentEvent arg0) {
        validate(arg0);
    }

    @Override
    public void insertUpdate(DocumentEvent arg0) {
        validate(arg0);
    }

    @Override
    public void changedUpdate(DocumentEvent arg0) {
        validate(arg0);
    }

    private void validate(DocumentEvent arg0){
        Boolean b = arg0.getDocument().getLength() == 11;
        if (!b) {
            l.setText("error");
        } else {
            l.setText("accepted");
        }
    }
});

In that case DcumentListener will validate each character entered or removed, and then change text in JLabel.

score 0 · Answer 2 · answered Dec 05 '13 at 11:07

You can do this using a JFormattedText field, there is a full tutorial here: http://docs.oracle.com/javase/tutorial/uiswing/components/formattedtextfield.html

and javadoc here: http://docs.oracle.com/javase/7/docs/api/javax/swing/JFormattedTextField.html

But in brief it is a way of setting up a text field and then specifying what the allowed data within that text field are and also what to do when someone tries to enter invalid data.

Check user has entered the correct number of symbols in a text field

2 Answers2