Java命令提示循环

Question

I have this simple code that works like a small command prompt. User is asked to enter a command and is displayed a message according to what he entered. I just want to make it loop so that the user is asked to enter a command again and again and again until he types 'exit'. How do I do that? Here is the code:

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();
}

Thank you

Answer 1

You can put it in a while loop like this:

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;
        }
}

Just let the condition for your while loop be while text <> "exit".

Answer 2

I prefer:

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 3

Something like this? I prefer do-while for this type of situation because you probably want to give at least one command.

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();
}

Answer 4

while loop is missing in the initial example:

    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 5

If you want to use a switch, easiest way would probably be a simple infinite while-loop with a label. When the input matches "exit" , we just break the loop.

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