如何关闭jframe面板或窗口

Question

I have 2 frames/windows, I have Exit button on window 2, an from window 1 I launch window 2 and then exit it ie setVisible(false);

When I execute window 2 I can easily click button exit and hide the current window, however when I launch window 2 from window 1, and then click exit button I get NullPointerException Error. then I instantiated it in the beginning with static and this error was gone, however the window 2 is not being closed/hidden its still there with no effect of button.

Window 1 code:

package com.my.jlms;

import java.awt.BorderLayout;
import java.awt.EventQueue;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import javax.swing.JButton;
import javax.swing.Icon;
import javax.swing.ImageIcon;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class LibrarianMenu extends JFrame {

private JPanel contentPane;
private static LibrarianMenu frame;


/**
 * Launch the application.
 */
public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                frame = new LibrarianMenu();
                frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}

/**
 * Create the frame.
 */
public LibrarianMenu() {
    setTitle("Librarian");
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setBounds(100, 100, 385, 230);
    contentPane = new JPanel();
    contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
    setContentPane(contentPane);
    contentPane.setLayout(null);

    JButton btnPasswd = new JButton("Change Pass");
    btnPasswd.setBounds(202, 76, 146, 39);
    contentPane.add(btnPasswd);


    btnPasswd.addActionListener(
            new ActionListener() {
                public void actionPerformed(ActionEvent e) {
                    ChangePwd framee = new ChangePwd();
                    framee.setVisible(true);
                }
            });

}

}

Window 2 Code:

package com.my.jlms;

import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;

import javax.swing.JButton;

public class ChangePwd extends JFrame {

private JPanel contentPane;
private static ChangePwd frame = new ChangePwd();;

private JButton btnExit;

/**
 * Launch the application.
 */
public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                frame = new ChangePwd();
                frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}

/**
 * Create the frame.
 */
public ChangePwd() {
    setResizable(false);
    setTitle("Password!");
    setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
    setBounds(100, 100, 266, 154);
    contentPane = new JPanel();
    contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
    setContentPane(contentPane);
    contentPane.setLayout(null);

    btnExit = new JButton("Exit");
    btnExit.setBounds(20, 80, 89, 30);
    contentPane.add(btnExit);


    btnExit.addActionListener(
            new ActionListener() {
                public void actionPerformed(ActionEvent ae) {
                    frame.setVisible(false);
                }
            });
}

}

Is there a solution I can set window 2 to hide ?

Answer 1

The problem here is that you are creating your frame, as your class, and not on the object frame , but you hide the frame which represents the object frame .

Change this line (in your actionListener's actionPerformed() method):

frame.setVisible(false);

to:

setVisible(false);

Answer 2

You can use dispose function for the purpose. see how dispose works.

Answer 3

If you want to close a JFrame, you could use the dispose() method.

Example:

public void actionPerformer(ActionEvent e)
{ 
  if(e.getSource().equals(closeFrameButton)
     {
        dispose();  //This will close the current JFrame
      }
}

NOTE: this is different to System.exit(0); . Using this will close the Java virtual machine. if you just want to close the frame, use dispose()