Question

我想要的只是登录一个简单的用户密码。

我已经放了一个ActionListener，当我按下登录时，只需弹出密码并检查它是否正常。

import java.awt.BorderLayout;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.GridLayout;
import java.awt.Insets;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JPasswordField;
import javax.swing.JTextField;

public class PasswordForm 
{
    private static String password = "mypass";
    public static void main(String[] args)
    {
        // Basic form create
        JFrame frame = new JFrame("Form 1");
        frame.setSize(300,300);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        // Creating the grid
        JPanel panel = new JPanel(new GridBagLayout());
        frame.getContentPane().add(panel, BorderLayout.NORTH);
        GridBagConstraints c = new GridBagConstraints();

        // Create some elements
        JTextField usernameInput = new JTextField(10);
        c.gridx = 0;
        c.gridy = 1;
        panel.add(usernameInput,c);

        JPasswordField passwordInput = new JPasswordField(10);
        c.gridx = 0;
        c.gridy = 2;
        panel.add(passwordInput,c);

        JButton loginInput = new JButton("Login");
        c.gridx = 0;
        c.gridy = 3;
        loginInput.addActionListener(new LoginButton());
        panel.add(loginInput,c);


        frame.setVisible(true);
    }

    static class LoginButton implements ActionListener
    {
        public void actionPerformed(ActionEvent e)
        {
            JTextField usernameInput = (JTextField)e.getSource();
            JOptionPane.showMessageDialog(null,"Text is:");
        }
    }
}

任何有帮助的人？

错误

    Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException: javax.swing.JButton
at PasswordForm$LoginButton.actionPerformed(PasswordForm.java:56)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

Answer 1

当您忽略代码存在编译错误并尝试运行它时，会发生以下异常。（我假设你正在使用Eclipse。在相关的源文件中查找红色错误标记，并检查Problems视图。）

    Exception in thread "AWT-EventQueue-0" java.lang.Error: 
        Unresolved compilation problem:
        The method getText() is undefined for the type ActionEvent

奇怪的是嵌入式编译错误消息似乎与您发布的源代码不对应。要么你改变了代码，要么你的构建过程中的一些缺陷会导致你运行陈旧的类文件。

其他几点：

您违反了嵌套类中的Java命名约定。类名应始终以大写字母开头。将“loginButton”更改为“LoginButton”。
您的PasswordForm课程过多地使用了static。 static内部类是正常的，但将password声明为静态，并将所有逻辑放入静态main方法将导致长期问题。（好吧，这段代码显然是实验性的......目前的形式。）

Answer 2

我希望这会对你有所帮助。

public class PasswordForm {

    private static String password = "mypass";
    private JTextField usernameInput;

    public PasswordForm() {
    }

    private void init(){
         // Basic form create
        JFrame frame = new JFrame("Form 1");
        frame.setSize(300,300);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        // Creating the grid
        JPanel panel = new JPanel(new GridBagLayout());
        frame.getContentPane().add(panel, BorderLayout.NORTH);
        GridBagConstraints c = new GridBagConstraints();

        // Create some elements
        usernameInput = new JTextField(10);
        c.gridx = 0;
        c.gridy = 1;
        panel.add(usernameInput,c);

        JPasswordField passwordInput = new JPasswordField(10);
        c.gridx = 0;
        c.gridy = 2;
        panel.add(passwordInput,c);

        JButton loginInput = new JButton("Login");
        c.gridx = 0;
        c.gridy = 3;
        loginInput.addActionListener(new LoginButton());
        panel.add(loginInput,c);


        frame.setVisible(true);
    }
    public static void main(String[] args){
       PasswordForm form = new PasswordForm();
       form.init();
    }

    class LoginButton implements ActionListener{

        public void actionPerformed(ActionEvent e){
            //JTextField usernameInput = (JTextField)e.getSource();
            String username = (usernameInput.getText().length()>0?usernameInput.getText():" U have not entered!");
            JOptionPane.showMessageDialog(null,"Text is : "+username);
        }
    }
}

Answer 3

不确定，但是：

JButton loginInput = new JButton("Login");
JTextField usernameInput = (JTextField)e.getSource();

事件的来源怎么可能是TextField？这将是事件起源的JButton。你需要重新设计这个，你的错误就会消失或变得更加清晰。

此外，Stephen C所说的：您提供的错误与您的代码不符。

Answer 4

这是@ tomdemuyt答案的附录，因为我只是很快就运行了你的代码。我得到了一个完全不同的错误：

Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException: javax.swing.JButton cannot be cast to javax.swing.JTextField
    at StupidCode$loginButton.actionPerformed(PasswordForm.java:54)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    ...more stack trace information that I'm not sure will help at this stage

我得到的例外只是将代码复制粘贴到Eclipse中，并添加了必要的导入。所以，正如@Stephen先前指出的那样，你的构建过程中一定有问题，或者如果你没有改变任何东西，那么你的项目设置可能不正确吗？

修改

好吧，我可以让代码做你想做的事。只是代码看起来并不是很好，并且已经过度依赖斯蒂芬所指出的静态类/方法。希望这只是您用来学习Java的实验代码......

如果您将JPasswordField设为私有和静态，即

private static JPasswordField passwordInput;
//main method below
//...
//main method finished, action listener follows...

在主要方法之外，您的ActionListener，loginButton可以“看到”它。这样，您可以执行类似

的操作

JOptionPane.showMessageDialog(null,"Text is: "+ new String(passwordInput.getPassword()));

但是这不是一个非常好的构建课程的方法。它有斯蒂芬指出的所有缺陷，可能更多因为我自己不是一个伟大的编码器。只要应该做你想要的东西，如果你想要快速解决问题。

Answer 5

当我按下按钮显示时，我只想要一个简单的对话框密码，在C＃中会很简单，但不是java ..

这在Java中可能和在C＃中一样简单，但您只熟悉一种语言。我对于初学者不知道如何在C＃中完成这项工作。无论如何，我稍微修改了你的代码以使其工作（我删除了修复的不相关部分以保持我的答案简短）

public class PasswordForm {
 private static String password = "mypass";
 public static void main(String[] args){
  //Swing operations should happen on the EDT
  EventQueue.invokeAndWait( new Runnable(){
        public void run(){
           //whole UI creation
           final JTextField usernameInput = new JTextField(10);
           final JPasswordField passwordInput = new JPasswordField(10);
           //more UI creation
           JButton loginInput = new JButton("Login");
           loginInput.addActionListener(new ActionListener(){
             public void actionPerformed(ActionEvent e){
               JOptionPane.showMessageDialog(null,"Username is:" + usernameInput.getText() + " Password is:" + passwordInput.getText());
             }
           });
        }
      } //todo catch the exceptions from the invokeAndWait call
  }
}

ClassCastException：javax.swing.JButton

5 个答案: