Java while循环无法按预期工作

Question

public static void main(String[] args) {
    boolean run = true;
    while (run) {
        Scanner kb = new Scanner(System.in);
        System.out.println("Welcome to MetricMan - the best converter in town!");
        System.out.println("Choose and option:");
        System.out.println("A) Fahrenheit to Celsius");
        System.out.println("B) Celcius to Fahrenheit");
        System.out.println("C) Miles to Kilometers");
        System.out.println("D) Kilometers to Miles");
        System.out.println("E) Inches to Centimeters");
        System.out.println("F) Centimeters to Inches");
        System.out.println("X) Quit the program");

        System.out.print("Your choice > ");
        String choice = kb.nextLine();

        double output; int input;
        System.out.print("Enter the number of ");
        switch (choice) { // do actions according to the user's choice. convert and display
        case "A":
            System.out.print("Farenheit > ");
            input = kb.nextInt();
            output = convertFtoC(input);
            System.out.println(input+" farenheit is "+output+" celsius");
            break;
        case "B":
            System.out.print("Celsius > ");
            input = kb.nextInt();
            output = convertCtoF(input);
            System.out.println(input+" celsius is "+output+" farenheit");
            break;
        case "C":
            System.out.print("miles > ");
            input = kb.nextInt();
            output = convertMtoK(input);
            System.out.println(input+" miles is "+output+" kilometres");
            break;
        case "D":
            System.out.print("kilometres > ");
            input = kb.nextInt();
            output = convertKtoM(input);
            System.out.println(input+" kilometres is "+output+" miles");
            break;
        case "E":
            System.out.print("inches > ");
            input = kb.nextInt();
            output = convertItoC(input);
            System.out.println(input+" inches is "+output+" centimeters");
            break;
        case "F":
            System.out.print("centimeters > ");
            input = kb.nextInt();
            output = convertCtoI(input);
            System.out.println(input+" centimeters is "+output+" inches");
            break;
        case "X":
            System.out.println(); System.out.println();
            System.out.println("May the odds be ever metric!");
            run = false;
            break;
        }
        System.out.println();
        kb.nextLine();
    }
} // end of main()

这是我的主要方法。 从代码中可以看出，输入X后，代码应立即停止运行，但是实际输出为

...
Your choice > X
Enter the number of 

May the odds be ever metric!

在实际的预期输出之前有一个“输入数字”，我认为没有理由在其中。 谁能帮忙解决此问题？

Answer 1

每次循环时都会出现该行。 解决此问题的一种方法是在每个case语句（X除外）中进行该调用。

Answer 2

在你的代码中

    System.out.print("Enter the number of ");

    switch (choice) { // do actions according to the user's choice. convert and display

因此，您基本上是在切换之前打印此内容，因此可以预期输出，您可能希望在内部实例而不是外部切换中调用它，当它的x退出时。

Answer 3

您正在做System.out.print("Enter the number of "); 在每种情况下。所以这就是为什么当您输入X时要进行打印，因此请尝试放入System.out.print("Enter the number of "); 在if(check if string entered is not X)内部if(check if string entered is not X)如下

if(!choice.equals("X")){
System.out.print("Enter the number of ");
}

要么

把System.out.print("Enter the number of "); 在每个开关盒内，如@Tanmoy所指