Java 命令提示符循环

Question

我有这个简单的代码，就像一个小的命令提示符。要求用户输入命令，并根据他输入的内容显示一条消息。我只是想让它循环，以便要求用户一次又一次地输入命令，直到他键入 'exit'。我怎么做？这是代码：

public static void main(String[] args) {

    Scanner command = new Scanner(System.in);

    System.out.println("Enter command: ");

    String text = command.nextLine();

        switch(text){

        case "start":
            System.out.println("Machine started!");
            break;

        case "stop":
            System.out.println("Machine stopped.");
            break;

        case "exit":
            System.out.println("Application Closed");
            break;

        default:
            System.out.println("Command not recognized!");
            break;
        }

    command.close();
}

谢谢

Answer 1

你可以像这样把它放在一个 while 循环中：

String text = "";

while(!text.equalsIgnoreCase("exit"))
{
    System.out.println("Enter command: ");

    text = command.nextLine();

        switch(text){

        case "start":
            System.out.println("Machine started!");
            break;

        case "stop":
            System.out.println("Machine stopped.");
            break;

        case "exit":
            System.out.println("Application Closed");
            break;

        default:
            System.out.println("Command not recognized!");
            break;
        }
}

只需让 while 循环的条件为 while text <> "exit"。

Answer 2

初始示例中缺少 while 循环：

    public static void main(String args[]) {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

    while (true) {
        String command = br.readLine().toLowerCase();

        switch (command) {
            case "exit": {
                // exit here
            } break;

            default: {
                // unrecognised command
            }
        }
    }
}

Answer 3

如果您想使用开关，最简单的方法可能是使用带有标签的简单无限 while 循环。当输入匹配 "exit" 时，我们就打破循环。

loop:
while (true) {
    String text = command.nextLine();
    switch (text) {
    // ...
    case "exit":
        break loop;
    }
}

Answer 4

我更喜欢：

public static void main(String[] args) {

    Scanner command = new Scanner(System.in);

    System.out.println("Enter command: ");
    boolean running = true;

    while(running){

        switch(command.nextLine()){

        case "start":
            System.out.println("Machine started!");
            break;

        case "stop":
            System.out.println("Machine stopped.");
            break;

        case "exit":
            System.out.println("Application Closed");
            running = false;
            break;

        default:
            System.out.println("Command not recognized!");
            break;
        }
    }
    command.close();
}

Answer 5

是这样的吗？对于这种情况，我更喜欢 do-while，因为您可能想要至少给出一个命令。

public static void main(String[] args) {
    boolean running = true;

    Scanner command = new Scanner(System.in);
    do {
        System.out.println("Enter command: ");
        String text = command.nextLine();
        switch(text){
            case "start":
                System.out.println("Machine started!");
                break;
            case "stop":
                System.out.println("Machine stopped.");
                running = false;  //here?
                break;
            case "exit":
                System.out.println("Application Closed");
                running = false; //..or here?
                break;
            default:
                System.out.println("Command not recognized!");
                break;
        }
    } while(running);
    command.close();
}

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