如何在java中创建循环回菜单的方法

Question

我正试图得到一个代码，它提供了几个选项供选择，虽然我可以让这些工作，但当我需要它返回到选项时，它会立即结束

public static void main(String[] args) {
    System.out.println("Hello, This is the math program");
    System.out.println("Select an application from below: \n");
    System.out.println("(1) pythagoraen");
    System.out.println("(2) Subtraction");
    System.out.println("(3) Multiplication");
    System.out.println("(4) Division");
    System.out.println("(5) Exit");
    System.out.println("What is your Choice? ");

    Scanner input = new Scanner(System.in);
    int choice = input.nextInt();
    if (choice == 1) {
        pythagoraen();
        System.out.println(pythagoraen());
    } if (choice == 2) {
        subtraction();
    } if (choice == 3) {
        multiplication();
    } if (choice == 4) {
        division();
    } if (choice == 5){
        exitprogam();
    }
}
public static void subtraction(){
    Scanner input = new Scanner( System.in );
    int number1;
    int number2;
    int difference;

    System.out.print( "Enter First integer: " );
    number1 = input.nextInt();
    System.out.print( "Enter Second integer: ");
    number2 = input.nextInt();

    difference = number1 - number2;
    System.out.printf( "The difference is %d\n", difference);

}

我尝试了几个不同的while循环，试图让它返回选项，但它要么无休止地循环，要么不起作用

编辑：我添加了其中一个方法作为示例。案例建议不起作用，因为我认为格式太不一样了

public static void main(String[] args) {
    System.out.println("Hello, This is the math program");
    System.out.println("Select an application from below: \n");
    System.out.println("(1) pythagoraen");
    System.out.println("(2) Subtraction");
    System.out.println("(3) Multiplication");
    System.out.println("(4) Division");
    System.out.println("(5) Exit");
    System.out.println("What is your Choice? ");

    Scanner input = new Scanner(System.in);
    int choice = input.nextInt();
    while(choice!=5){
        if (choice == 1) {
            pythagoraen();
            System.out.println(pythagoraen());
        } if (choice == 2) {
            subtraction();
        } if (choice == 3) {
            multiplication();
        } if (choice == 4) {
            division();
        } if (choice == 5){
            exitprogam();
        }
}}

这是我唯一可以运行的while代码。它无限地自我循环

Answer 1

实现这一点的方法有很多，但更好的方法是使用开关。使用switch语句，您可以有许多执行路径，这些路径似乎比使用while循环更适合这种情况。然而，while循环和switch语句实际上不能在效率方面进行比较，因为它们从根本上是不同的，如本article所示。以下是交换机的实现情况：

public static void main(String[] args) {
    int exitFlag = 0;
    int choice = showMenu();

     do {
            switch (choice) {
            case 1:
                System.out.println("pythagoraen()");
                break;
            case 2:
                System.out.println("subtraction()");
                break;
            case 3:
                System.out.println("multiplication()");
                break;
            case 4:
                System.out.println("division()");
                break;
            case 5:
                System.out.println("exitprogam()");
                exitFlag = 1; 
                break;
            default: 
                System.out.println("Invalid Option()");

                break;
            }
        if (exitFlag != 1) {
            choice = showMenu();    
        }

      }while (choice != 5);
}

private static int showMenu() {
    System.out.println("Hello, This is the math program");
    System.out.println("Select an application from below: \n");
    System.out.println("(1) pythagoraen");
    System.out.println("(2) Subtraction");
    System.out.println("(3) Multiplication");
    System.out.println("(4) Division");
    System.out.println("(5) Exit");
    System.out.println("What is your Choice? ");

    Scanner input = new Scanner(System.in);
    int choice = input.nextInt();
    return choice;
}

从长远来看，这对于重构来说更干净、更容易。有关交换机的更多信息，请参阅oracle docs

Answer 2

你需要把你需要做的事情一次又一次地循环起来

public static void main(String[] args) {
    System.out.println("Hello, This is the math program");
    System.out.println("Select an application from below: \n");
    System.out.println("(1) pythagoraen");
    System.out.println("(2) Subtraction");
    System.out.println("(3) Multiplication");
    System.out.println("(4) Division");
    System.out.println("(5) Exit");
    System.out.println("What is your Choice? ");

    Scanner input = new Scanner(System.in);
    int choice = input.nextInt();
    while(choice!=5){
        if (choice == 1) {
            pythagoraen();
        }
        else if (choice == 2) {
            subtraction();
        }
        else if (choice == 3) {
            multiplication();
        }
        else if (choice == 4) {
            division();
        }
        System.out.println("What is your next Choice? ");
        choice = input.nextInt();
    }
}

如果您需要再次打印菜单，那么您也可以将其放入循环中。在这里，你要做的是请求用户输入，然后选择你想要做的操作。最后，再次询问用户下一步要做什么。如果用户输入5，while条件变为false并退出循环

我还删除了if choice == 5条件，因为while循环将处理该场景。在第一个if之后的每个if之前还添加了else。这是为了提高效率，所以如果它与第一个匹配，它不会检查其余的匹配项

Answer 3

用while循环试试这个

Scanner input = new Scanner(System.in);
int choice = input.nextInt();
while(choice != 5) {
Scanner input = new Scanner(System.in);
int choice = input.nextInt();
    if (choice == 1) {
        pythagoraen();
        System.out.println(pythagoraen());
    } if (choice == 2) {
        subtraction();
    } if (choice == 3) {
        multiplication();
    } if (choice == 4) {
        division();
    } if (choice == 5){
        exitprogam();
    }
}

Answer 4

要实现你想要做的事情，最好的办法是使用do While循环。注意你请求输入的位置，然后如果选择与你的停止条件相等，将其作为条件放在循环的while部分

While循环将运行0-N次，而Do-While循环总是执行1-N次。利用这个优势

这是一个很好的参考： https://docs.oracle.com/javase/tutorial/java/nutsandbolts/while.html