如何在switch语句中创建actionPerformed？

Question

我正在尝试用基于命令提示符的GUI创建一个简单的程序(即输入命令并单击enter按钮)。每当用户单击enter按钮时，都会处理他们在JTextArea中键入的所有信息，然后根据他们的输入(例如键入/exit关闭程序)给出一个输出。

每当用户在/exit中键入时，都会出现一个提示，询问用户是否确定要退出。但是，一旦弹出，如果用户输入了未被识别的内容，它就会被我输入的无效输入消息所取代。发生这种情况的唯一原因是，ActionListener类仍然将/exit存储在inputHolder字符串中，这是我用来存储用户输入并对其进行处理的字符串。

package msai;

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

public class MainFrame extends JFrame implements ActionListener {
    JTextArea output;
    JButton inputButton;
    JTextArea commandLine;
    String inputHolder;
    String invalid = "Invalid input!";

    public MainFrame() {
        super("MSAI");
        setLookAndFeel();
        setSize(650, 350);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        FlowLayout flo = new FlowLayout();
        setLayout(flo);

        output = new JTextArea("Hi! I'm MSAI. Type any command to get started, or type /help for a list of commands and syntax!", 8, 40);
        inputButton = new JButton("ENTER");
        inputButton.addActionListener(this);
        commandLine = new JTextArea(8, 40);
        commandLine.setLineWrap(true);
        commandLine.setWrapStyleWord(true);
        JScrollPane scroll = new JScrollPane(commandLine, JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);

        add(output);
        add(inputButton);
        add(scroll);

        setVisible(true);

    }

    public void actionPerformed(ActionEvent event) {

        inputHolder = commandLine.getText();
        switch(inputHolder) {
            "/exit":
                output.setText("Are you sure you want to terminate this session?");
                inputHolder = commandLine.getText();
                switch(inputHolder.toUpperCase()) {
                    case "YES":
                        System.exit(0);
                        break;
                    case "NO":
                        output.setText("Your session has not been terminated.");
                        break;
                    default:
                        output.setText(invalid);
                        break;
            }
        } 
    }  
    private void setLookAndFeel() {
        try {
            UIManager.setLookAndFeel(
            "javax.swing.plaf.nimbus.NimbusLookAndFeel"
            );
        } catch (Exception exc) {
            //ignore error
        }
    }


    public static void main(String[] args) {
        MainFrame frame = new MainFrame();
    }
}

目前，我唯一想到的解决方法就是在/exit switch语句中放入另一个actionPerformed，但我不确定如何做到这一点，或者这是否是最好的解决方案。我欢迎任何答案和反馈，只是请不要有毒！

Answer 1

当你这样做的时候

output.setText("Are you sure you want to terminate this session?");
inputHolder = commandLine.getText();

用户尚未更新commandLine并按下按钮，因此没有任何变化。您需要“等待”，直到用户再次响应。

您需要将请求的“状态”带到下一次调用ActionPerformed时，例如...

private boolean wantsToExit = false
public void actionPerformed(ActionEvent event) {

    inputHolder = commandLine.getText();

    if (wantsToExit) {
        if (wantsToExit && inputHolder.equals("YES")) {
            // Better to close the frame and let the system deal with it
        } else if (wantsToExit && inputHolder.equals("NO")) {
            output.setText("Your session has not been terminated.");
        }
        wantsToExit = false;
    } else {
        switch(inputHolder) {
            "/exit":
                wantsToExit = true;
                output.setText("Are you sure you want to terminate this session?");
                break;
        } 
    }  
}

如果您希望在单个流中执行此操作，则应考虑使用JOptionPane来提示用户

Answer 2

问题是actionPeformed中的代码是完全执行的，用户无法输入是或否，然后单击"ENTER“按钮。内部开关使用值为"/exit“的inputHolder执行，这导致了默认情况。

您需要一种方法来区分这些操作。您可以使用标志来指示用户是否已发出退出命令。如果标志为true，则执行内部开关。否则，从该方法返回。

这里的代码试图接近你最初的想法。

    boolean exitCommand = false;  //has the user issued exit command?


    public void actionPerformed(ActionEvent event) {
        inputHolder = commandLine.getText();
        if (exitCommand){
            switch (inputHolder.toUpperCase()) {
                    case "YES":
                        System.exit(0);
                        break;
                    case "NO":
                        exitCommand = false; //forget exit command.
                        output.setText("Your session has not been terminated.");
                        break;
                    default:
                        output.setText(invalid);
                        break;
                }
        }


        switch (inputHolder) {
            case "/exit": 
                exitCommand = true;
                commandLine.setText("");
                output.setText("Are you sure you want to terminate this session?");
                inputHolder = commandLine.getText();
                if (!exitCommand) {
                    exitCommand = true;
                    return;
                }  

        }
    }