How to limit the number of digits in a JPasswordField in Java?

Question

I have my Java code working in Eclipse but I need to add a few functionnality.

First, how to limit the number of digits that can be entered by the user ? Actually I

Answer 1

JPasswordField limit characters to 4

private void edtPinCodeKeyReleased(java.awt.event.KeyEvent evt) {                                       
    if (String.valueOf(edtPinCode.getPassword()).trim().length() > 4) 
        edtPinCode.setText(String.valueOf(edtPinCode.getPassword()).trim().substring(0, 4));
} 

Answer 2

How can I play with the size of the JPassword box ? Is there a way to modify it just like a JTextField for example ? Because my line "p1.setPreferredSize(new Dimension(100, 25));" does not seem to really let me modify the size of the box.

Don't use setPrefferedSize() instead use this constructor JPasswordField(int col) .Read more about that here Should I avoid the use of set(Preferred|Maximum|Minimum)Size methods in Java Swing?

How to limit the number of digits that can be entered by the user ? Actually I have a JPasswordField that let a person enter a pin Code, and I would like this JPasswordField limited to 4 digits maximum. So how to stop the input as soon as 4 digits are entered ?

For limit input you can use DocumentFilter as shown in example below.

 public class JPasswordFieldTest {

    private JPanel panel;

    public JPasswordFieldTest() {
        panel = new JPanel();
        //set horizontal gap
        ((FlowLayout) panel.getLayout()).setHgap(2);

        panel.add(new JLabel("Enter pin :"));
        JPasswordField passwordField = new JPasswordField(4);
        PlainDocument document = (PlainDocument) passwordField.getDocument();
        document.setDocumentFilter(new DocumentFilter() {

            @Override
            public void replace(DocumentFilter.FilterBypass fb, int offset, int length, String text, AttributeSet attrs) throws BadLocationException {
                String string = fb.getDocument().getText(0, fb.getDocument().getLength()) + text;

                if (string.length() <= 4) {
                    super.replace(fb, offset, length, text, attrs); //To change body of generated methods, choose Tools | Templates.
                }
            }

        });
        panel.add(passwordField);
        JButton button = new JButton("OK");
        panel.add(button);

    }

    public static void main(String[] args) {
        //Schedule a job for the event-dispatching thread:
        //creating and showing this application's GUI.
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI("Password Example");
            }
        });

    }

    private static void createAndShowGUI(String str) {
        JFrame frame = new JFrame(str);
        frame.setDefaultCloseOperation(EXIT_ON_CLOSE);
        JPasswordFieldTest test = new JPasswordFieldTest();
        frame.add(test.panel);
        frame.pack();
        frame.setVisible(true);
    }

}

Answer 3

First, how to limit the number of digits that can be entered by the user ?

• See this Q&A: How To limit the number of characters in JTextField? As JPasswordField extends from JTextField it should perfectly work.
• As @nachokk correctly pointed out, working with document filters (like he does in his answer) is a more flexible option. You can read more about it in Concepts: About Documents and Implementing a Document Filter sections of Text Component Features official article.

Then, how can I play with the size of the JPassword box ? Is there a way to modify it just like a JTextField for example ? Because my line "p1.setPreferredSize(new Dimension(100, 25));" does not seem to really let me modify the size of the box.

• Don't set fixed sizes when you're working with Swing. See this topic: Should I avoid the use of set(Preferred|Maximum|Minimum)Size methods in Java Swing?.
• You can use setColumns(int columns) instead to indicate the preferred size of the text field.
• See How to Use Password Fields tutorial.

Answer 4

Generalize code and Easy Way to solve this question

Four Digit limit the number in a JPasswordField (Java) using netbeans..

//JPasswordField Variable name is "Password_Field_Demo"
//Jlabel variable name is "lbl_register"

public class Register extends javax.swing.JFrame {
    static int count=1;     //static variable(count) initialize on first time..

//Default Constructor
public Register() {
    initComponents();
}

//KeyTyped(KeyEvent evt) Method in Password_Field_Demo
private void Password_Field_DemoKeyTyped(java.awt.event.KeyEvent evt) {                                    
    char c = evt.getKeyChar(); //get the Character
    if(Character.isDigit(c))  //isDigit() method on Character and Enter only Digit or number
    {
        if(count>4)
        {                    
            evt.consume();//Greater than Four Digit to consume()method ..Not Input more than Four Digit
            lbl_register.setText(" Maximum Four Digit Allowed..");
        }
        else{
            count++;
            lbl_register.setText("");
        }
    }
    if((c == KeyEvent.VK_BACK_SPACE) ||(c == KeyEvent.VK_DELETE))
    {
        if(count>1)
            count--;
        lbl_register.setText("");
    }

   //lbl_register.setText(" count :"+count);


}  //End Password_Field_DemoKeyTyped()