Question

我有2个问题。 1.如果用户没有在控制台中输入正确的命令，我有一个问题就是在'do，while循环'中找到退步的方法。 2.执行此操作后，我想在开关循环中使用用户输入，因此可以处理所选命令，但我不确定将哪些内容放入括号中作为要测试的变量，因为它无法识别用户输入。

这是我到目前为止所做的。我已经尝试了很多东西，但没有尝试过。

  `package assignment6;
   public class Enumeracija {

   public enum Commands {
   PROPERTIES, NEW_FOLDER, RENAME, COPY, CUT, DELETE, UNSPECIFIED 
   }}  



   package assignment6;
   import assignment6.Enumeracija.Commands;
   import java.io.*;
   import java.util.Scanner;
   public class Assignment6 {
   public static boolean main(String[] args) throws FileNotFoundException, 
   IOException {

    //Showing commands to user
    for (int i = 0; i<Commands.values().length-1; i++){
        System.out.println(Commands.values()[i]);
    }
    //Reading users input

        Scanner scan = new Scanner(System.in); 
        System.out.println("Enter one of the given commands: ");
        String userInput;
    /* WHILE DO LOOP so user can make a mistake and program will not stop 
    running, until he writes it correctly. But Im getting main class not 
    found problem, when I want to run it.*/ 
    do {
        userInput = scan.nextLine().trim().toUpperCase();

        if (userInput.equals(Commands.values())) {
        return true;} 
        else {
        System.out.println("Input error. Keep trying and make sure you write command correctly.");    
        return false;}
    } while (false);

    switch(userInput) {
    /*If I use userInput, it does not recognise commands 
    that user enters. Every case is being unrecognized.*/ 
        case PROPERTIES:
        //;
        break;
        case NEW_FOLDER:
        //;
        break;
        case RENAME:
        //;
        break;
        case COPY:
        //;
        break;
        case CUT:
        //;
        break;
        case DELETE:
        //;
        break;
        case UNSPECIFIED: 
        //;
        break;*/

Answer 1

首先，Java中main方法的返回类型应该总是无效。

public static void main(String[] args) throws FileNotFoundException, IOException

其次，如果用户输入了正确的命令，程序将在您使用return语句时结束。如果你使用一个布尔变量作为标志，将其值设置为true并且只是突破循环，那就更好了。

boolean flag = false;

do {
    userInput = scan.nextLine().trim().toUpperCase();

    if (userInput.equals(Commands.values())) {
    flag = true;
    break;} 
    else {
    System.out.println("Input error. Keep trying and make sure you write command correctly.");    
    }
} while (flag);

这将使用户保持循环，直到输入正确的命令。

现在，来到switch语句，因为命令是enums的形式，你需要正确引用它们。

switch(userInput) {
    case Commands.PROPERTIES:
    //;
    break;
    case Commands.NEW_FOLDER:
    //;
    break;
    case Commands.RENAME:
    //;
    break;
    case Commands.COPY:
    //;
    break;
    case Commands.CUT:
    //;
    break;
    case Commands.DELETE:
    //;
    break;
    case Commands.UNSPECIFIED: 
    //;
    break;

让我知道这是否有效。

Answer 2

您正在通过返回true / false来停止程序流程。而是维护变量以跟踪

 do {
        boolean validInput = false; // this will keep track
        userInput = scan.nextLine().trim().toUpperCase();
        if (userInput.equals(Commands.values())) {
           validInput = true; // make flag as true on valid input
        } 
        else {
           System.out.println("Input error. Keep trying and make sure you write command correctly.");    
           validInput = false; // make flag as false on invalid input
       }
    } while (!validInput); //repeat the loop if invalid input

switch语句的问题在于您要将String传递给switch，而案例是Enums。将String转换为Enum对象

Commands value = Commands.valueOf(userInput);

switch(value){
   //processing
}

Answer 3

do {
    userInput = scan.nextLine().trim().toUpperCase();
    // telling you what to do here will take the entire fun out of the problem
    // HINT: check what Command.values() actually does and also what userInput.equals() actually does.
    // HINT: once you have figured out how to interpret the user input, you need to store it in a variable to be used in the switch statement
    // HINT: the variable that you store it in should be of the Command type (this should be more than sufficient a hint)
    if (userInput.equals(Commands.values())) {
        // do not return here. Return will cause the execution of the main method to stop
        // what you actually want over here is break;
        // this will allow you to break out of the infinite loop once your conditions are met.
    } 
    else {
        System.out.println("Input error. Keep trying and make sure you write command correctly.");   
        // remove the return condition here. This will stop execution of the main method
    }
} while (true); // change condition to true so that loop is infinite

Answer 4

您可以使用while循环而不是do while循环。这使代码更易读，因此更容易调试。

boolean flag = true;
while(flag){
 userInput = scan.nextLine().trim().toUpperCase();
 if (userInput.equals(Commands.values())) 
     flag = false;
 else 
     System.out.println("Input error..."); 
}

您正在使用userInput，它是switch语句中的String对象。 Click here有关此的解释。

主要类的签名是：

public static void (String[] whateverHere)

Scanner.nextLine（）在do，while循环中。退一步

4 个答案: