java - How to UnFocus a JTextField

Question

When my application loads, which is made using netbeans, the first JTextField is automatically focused, and in this JTextField, I have written "Enter your Username", it will go away when the user clicks on this field, but when the application is loaded, this field is focused, means I can't see "Enter your Username", how to unfocus it on startup ?

Answer 1

A log-in would be best done in a modal dialog, but that introduces problems in that the method requestFocusInWindow() must be called after the component is visible, but that is blocked by the fact the dialog is modal!

This example uses Rob Camick's RequestFocusListener (as presented in Dialog Focus) to manage focus after the dialog is visible.

Note: That is how it appears before the user does anything. The password field is focused by default.

import java.awt.*;
import javax.swing.*;
import javax.swing.event.*;

public class LoginRequired {

    LoginRequired() {
        JFrame f = new JFrame("Login Required");
        f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

        f.setResizable(false);
        f.setSize(400, 300); // not recommended, but used here for convenience
        f.setLocationByPlatform(true);
        f.setVisible(true);

        showLogin(f);
    }

    private void showLogin(JFrame frame) {
        JPanel p = new JPanel(new BorderLayout(5,5));

        JPanel labels = new JPanel(new GridLayout(0,1,2,2));
        labels.add(new JLabel("User Name", SwingConstants.TRAILING));
        labels.add(new JLabel("Password", SwingConstants.TRAILING));
        p.add(labels, BorderLayout.LINE_START);

        JPanel controls = new JPanel(new GridLayout(0,1,2,2));
        JTextField username = new JTextField("Joe Blogs");
        controls.add(username);
        JPasswordField password = new JPasswordField();
        password.addAncestorListener(new RequestFocusListener(false));
        controls.add(password);
        p.add(controls, BorderLayout.CENTER);

        JOptionPane.showMessageDialog(
            frame, p, "Log In", JOptionPane.QUESTION_MESSAGE);
        System.out.println("User Name: " + username.getText());
        System.out.println("Password: " + new String(password.getPassword()));
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            new LoginRequired();
        });
    }
}

/**
 *  Convenience class to request focus on a component.
 *
 *  When the component is added to a realized Window then component will
 *  request focus immediately, since the ancestorAdded event is fired
 *  immediately.
 *
 *  When the component is added to a non realized Window, then the focus
 *  request will be made once the window is realized, since the
 *  ancestorAdded event will not be fired until then.
 *
 *  Using the default constructor will cause the listener to be removed
 *  from the component once the AncestorEvent is generated. A second constructor
 *  allows you to specify a boolean value of false to prevent the
 *  AncestorListener from being removed when the event is generated. This will
 *  allow you to reuse the listener each time the event is generated.
 */
class RequestFocusListener implements AncestorListener
{
    private boolean removeListener;

    /*
     *  Convenience constructor. The listener is only used once and then it is
     *  removed from the component.
     */
    public RequestFocusListener()
    {
        this(true);
    }

    /*
     *  Constructor that controls whether this listen can be used once or
     *  multiple times.
     *
     *  @param removeListener when true this listener is only invoked once
     *                        otherwise it can be invoked multiple times.
     */
    public RequestFocusListener(boolean removeListener)
    {
        this.removeListener = removeListener;
    }

    @Override
    public void ancestorAdded(AncestorEvent e)
    {
        JComponent component = e.getComponent();
        component.requestFocusInWindow();

        if (removeListener)
            component.removeAncestorListener( this );
    }

    @Override
    public void ancestorMoved(AncestorEvent e) {}

    @Override
    public void ancestorRemoved(AncestorEvent e) {}
}