如何在扫描仪中使用枚举类型

Question

非常感谢你在adv的帮助！

使用枚举类型的扫描仪时出错。但是我不允许在此任务中使用Buffer（InputStreamReader）。围绕它的最佳工作是什么？

我收到以下错误：

Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
Cannot switch on a value of type String for source level below 1.7. Only convertible int values or enum variables are permitted

at ui.Application.runCLI(Application.java:33)
at ui.Application.main(Application.java:13)

代码：

package ui;

import java.util.Scanner;

公共类申请{

static String command;

public enum Command {
    CONNECT, DISCONNECT, SEND, LOGLEVEL, HELP, QUIT, EXIT
}

private static void run(Scanner sc) {
    // String command; // ready for the input

    boolean done = false; // ready for the menu loop
    while (!done) { // keep on until done

        System.out
                .println("Milestone1: Connection and interation with TCP server");
        System.out
                .println("-------------------Please select on of the commandso-------------------------------------");
        System.out.println("connect");
        System.out.println("disconnect");
        System.out.println("send");
        System.out.println("logLevel");
        System.out.println("help");
        System.out.println("quit");
        System.out.println("exit");

        command = sc.nextLine(); // take user input         
        Command cmd=null;
        try{
        cmd=Command.valueOf(command.toUpperCase());
        }
        catch (IllegalArgumentException e){
            System.out.println("Invalid input");
            return;
        }
        switch (cmd) {

        case EXIT: // exit menu
            done = true;// condition for breaking the loop
            break;

        case CONNECT:

            System.out.print(" IP adress: ");

            try {
                String userInput = sc.toString(); // user Input

                System.out.println(" Port: ");

                int userInput1 = sc.nextInt();// user Input

                if (userInput1 >= 0) {

                    System.out.println(" EcoClient>" + " " + command + " "
                            + userInput + " " + userInput1);
                } else {
                    System.out
                            .println("Entered value for Port is negative number or IP adress length < 7 || > 15, not in n.n.n.n format ");
                }

            }

            catch (Exception e) {// throw exception in case of illogical
                                    // input
                System.out.println("\nBad input, please try again ");
                sc.nextLine(); // remove leftover "\n"
            }

            break;

        case DISCONNECT:

            System.out.println(" EcoClient>" + " " + command);

            break;

        case SEND:

            System.out
                    .println("Please enter " + " Hello World " + "phrase");
            try {
                String userInput = sc.toString(); // user Input
                System.out.println(" EcoClient>" + " " + command + " "
                        + userInput);

            }

            catch (Exception e) {// throw exception in case of illogical
                                    // input

                System.out.println("\nBad input, please try again ");
                sc.nextLine(); // remove leftover "\n"
            }
            break;

        case LOGLEVEL:
            try {
                System.out.println(" EcoClient>" + " " + command + "< "
                        + "current log status" + " >");
            }

            catch (Exception e) {// throw exception in case of illogical
                                    // input

                System.out.println("\nBad input, please try again ");
                sc.nextLine(); // remove leftover "\n"

            }
            break;

        case HELP:
            try {
                System.out
                        .println("Following set of commands provide following functionalities:"
                                + " connect: establishes connection to the eco server "
                                + "disconnect: disconnects from the server and receives confirmation message "
                                + "send: sends the message to the server "
                                + "logLevel: prints out current log status"
                                + "quit: quits and notifies user about program shut down "
                                + "exit: cancel the input");

            }

            catch (Exception e) {// throw exception in case of illogical
                                    // input

                System.out.println("\nBad input, please try again ");
                sc.nextLine(); // remove leftover "\n"
            }
            break;

        case QUIT:

            try {
                System.out.println(" EcoClient> " + command);

            }

            catch (Exception e) {// throw exception in case of illogical
                                    // input

                System.out.println("\nBad input, please try again ");
                sc.nextLine(); // remove leftover "\n"

            }
            break;

        default:
            System.out.println("Does not recognise "
                    + "the input, pl. try again");

        }

    }
}

public static void main(String[] args)  {

    Scanner sc = new Scanner(System.in);// will take user input

    run(sc);

}

}

Answer 1

sc.nextLine()返回一个String。您将需要使用静态方法Command将其转换为switch的实例（您正在使用Command.valueOf(String)），该方法解析字符串并返回匹配的Command实例

以下是基础知识：

command = sc.nextLine(); // take user input
Command cmd = null;
try {
    cmd = Command.valueOf(command.toUpperCase());
} catch (IllegalArgumentException e) {
    System.out.println("Invalid input, sorry."); //This is given on invalid input.  Put whatever type of error message you want here.
    return;
}
switch (cmd) {
//...