java - 无法关闭 Windows 并打开其他窗口

Question

我正在使用 Java8，并且我正在尝试使用代码从一个框架移动到另一个框架。

问题:第一个 JPanel 未关闭当我尝试关闭窗口时，第二个 JPanel 出现错误

错误消息:

线程“AWT-EventQueue-0”中出现异常 java.lang.NullPointerException 在 ex2.Main2$2.actionPerformed(Main2.java:60) 在 javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022) 在 javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348) 在 javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402) 在 javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259) 在javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252) 在 java.awt.Component.processMouseEvent(Component.java:6539) 在 javax.swing.JComponent.processMouseEvent(JComponent.java:3324) 在 java.awt.Component.processEvent(Component.java:6304) 在 java.awt.Container.processEvent(Container.java:2239) 在java.awt.Component.dispatchEventImpl(Component.java:4889) 在 java.awt.Container.dispatchEventImpl(Container.java:2297) 在 java.awt.Component.dispatchEvent(Component.java:4711) 在java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4904) 在java.awt.LightweightDispatcher.processMouseEvent(Container.java:4535) 在java.awt.LightweightDispatcher.dispatchEvent(Container.java:4476) 在 java.awt.Container.dispatchEventImpl(Container.java:2283) 在java.awt.Window.dispatchEventImpl(Window.java:2746) 在 java.awt.Component.dispatchEvent(Component.java:4711) 在 java.awt.EventQueue.dispatchEventImpl(EventQueue.java:760) 在java.awt.EventQueue.access$500(EventQueue.java:97) 在 java.awt.EventQueue$3.run(EventQueue.java:709) 在 java.awt.EventQueue$3.run(EventQueue.java:703) 在 java.security.AccessController.doPrivileged( native 方法) 在 java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74) 在 java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:84) 在 java.awt.EventQueue$4.run(EventQueue.java:733) 在 java.awt.EventQueue$4.run(EventQueue.java:731) 在 java.security.AccessController.doPrivileged( native 方法) 在 java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74) 在 java.awt.EventQueue.dispatchEvent(EventQueue.java:730) 在 java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:205) 在 java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116) 在java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105) 在 java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101) 在 java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93) 在 java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

请帮忙。

第一帧:

public class ex2 {

    private JFrame frmLogin;
    private JTextField textField;
    private JPasswordField passwordField;

//cuted the methods to start the frame

    private void initialize() {
        frmLogin = new JFrame();
        frmLogin.getContentPane().setFont(new Font("Dialog", Font.BOLD, 18));
        frmLogin.setTitle("Login");
        frmLogin.setBounds(100, 100, 400, 300);
        frmLogin.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frmLogin.getContentPane().setLayout(null);

        JLabel lblUserName = new JLabel("Username");
        lblUserName.setBounds(130, 40, 150, 15);
        lblUserName.setFont(new Font("Dialog", Font.BOLD, 18)); 
        frmLogin.getContentPane().add(lblUserName);

        JLabel lblPassword = new JLabel("Password");
        lblPassword.setBounds(130, 100, 150, 15);
        lblPassword.setFont(new Font("Dialog", Font.BOLD, 18));
        frmLogin.getContentPane().add(lblPassword);

        textField = new JTextField();
        textField.setBounds(130, 70, 150, 19);
        textField.setFont(new Font("Dialog", Font.BOLD, 18));
        frmLogin.getContentPane().add(textField);
        textField.setColumns(10);

        passwordField = new JPasswordField();
        passwordField.setBounds(130, 130, 150, 19);
        passwordField.setFont(new Font("Dialog", Font.BOLD, 18));
        frmLogin.getContentPane().add(passwordField);

        JButton btnLogin = new JButton("Login");
        btnLogin.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                String user = textField.getText();
                String pass = String.copyValueOf(passwordField.getPassword());

                if (user.equals("Rod") && pass.equals("123")) {
                    Main2 segundo = new Main2();

                    segundo.setVisible(true);
                    ex2.setVisible(false);

                }
            }
        });
        btnLogin.setBounds(130, 190, 150, 25);
        btnLogin.setFont(new Font("Dialog", Font.BOLD, 18));
        frmLogin.getContentPane().add(btnLogin);

}

第二帧

public class Main2 extends JFrame {

    private JPanel contentPane;
    private static Main2 frame2;

    public Main2() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 400, 300);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        setContentPane(contentPane);
        contentPane.setLayout(null);

        JLabel lblEntramos = new JLabel("Entramos");
        lblEntramos.setFont(new Font("Dialog", Font.BOLD, 22));
        lblEntramos.setBounds(150, 100, 200, 15);
        contentPane.add(lblEntramos);

        JButton btnSair = new JButton("Sair");
        btnSair.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {             
                frame2.setVisible(false);
            }
        });     
        btnSair.setBounds(125, 175, 150, 25);
        contentPane.add(btnSair);           
    }
}

Answer 1

我使用以下代码复制了您的登录表单，但没有收到任何错误..

import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JPasswordField;
import javax.swing.JTextField;
import javax.swing.border.EmptyBorder;

public class ex3 extends JFrame {

    public JPanel contentPane;
    private JTextField textField;
    private JPasswordField passwordField;


    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    ex3 frame = new ex3();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the frame.
     */
    public ex3() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 450, 300);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        setContentPane(contentPane);
        contentPane.setLayout(null);



        JLabel lblUserName = new JLabel("Username");
        lblUserName.setBounds(130, 40, 150, 15);
        lblUserName.setFont(new Font("Dialog", Font.BOLD, 18));
        contentPane.add(lblUserName);

        JLabel lblPassword = new JLabel("Password");
        lblPassword.setBounds(130, 100, 150, 15);
        lblPassword.setFont(new Font("Dialog", Font.BOLD, 18));
        contentPane.add(lblPassword);

        textField = new JTextField();
        textField.setBounds(130, 70, 150, 19);
        textField.setFont(new Font("Dialog", Font.BOLD, 18));
        contentPane.add(textField);
        textField.setColumns(10);

        passwordField = new JPasswordField();
        passwordField.setBounds(130, 130, 150, 19);
        passwordField.setFont(new Font("Dialog", Font.BOLD, 18));
        contentPane.add(passwordField);

        JButton btnLogin = new JButton("Login");
        btnLogin.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                String user = textField.getText();
                String pass = String.copyValueOf(passwordField.getPassword());

                if (user.equals("Rod") && pass.equals("123")) {
                    Main2 segundo = new Main2();

                    segundo.setVisible(true);
                    setVisible(false);

                }
            }
        });
        btnLogin.setBounds(5, 196, 424, 60);
        btnLogin.setFont(new Font("Dialog", Font.BOLD, 18));
        contentPane.add(btnLogin);
    }

}

您确定您“剪切”的表单代码没有犯任何错误吗？