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我是 Java 和这个网站的新手，所以请原谅我可能犯的任何错误，我无能为力！

我正在尝试制作一个程序来计算通过不同介质的声速。到目前为止，程序将要求用户输入距离并允许输入，对于媒体也是如此。我创建了几个案例来计算给定媒体的正确工作的答案。

问题是当我尝试创建一个循环来识别媒体输入是否不是可用的 4 个选项之一时。我能够成功地创建一个循环来识别距离输入是否不是数值，并尝试对中等输入使用类似的原则，但要么一直卡在无限循环中，要么在我输入时收到我为错误条目创建的消息正确的选择。我已经尝试过我所学过的基本循环：for、do-while 等，但我被卡住了。任何和所有的建议都非常感谢，非常感谢！

public static void main(String[] args) {
    //prompt the user about the purpose of this program

    System.out.println(" The purpose of this program is to calculate the speed of sound through several mediums.\n The program user will input a distance in feet followed by a mediums and the program will output the speed in feet per second and miles per hour\n");
    //declare variables

    Scanner keyboard = new Scanner(System.in);

    final double Air = 1126.1;

    final double Water = 4603.2;

    final double Steel = 20013.3;

    final double Earth = 22967.4;

    double OneFootPerSecond = .68181818182;

    double Distance;

    double AirSpeed;

    double WaterSpeed;

    double SteelSpeed;

    double EarthSpeed;

    System.out.print(" What is the distance in feet:" );
    //ask the user to input variables


        while (!keyboard.hasNextDouble()){
        System.out.println("Please enter a valid numeric value, try again: ");
        keyboard.next();
        }
        Distance =keyboard.nextDouble();
        {
        System.out.print("Input the media: Air, Water, Steel, or Earth: ");
        String Input = keyboard.next();   
        Input.toLowerCase();

        switch (Input)

         {

            case "air":
            AirSpeed = Distance/Air;
            System.out.print("\n \nThe time to for sound to travel ");
            System.out.print(Distance);
            System.out.print(" feet through AIR" +"\n");
            System.out.printf("%.6f", AirSpeed);
            System.out.print(" seconds or ");
            System.out.printf("%.1f", OneFootPerSecond*Air);
            System.out.print(" miles per hour."); 
            System.out.print("\n \nEnter Yes for another calculation, else No: ");
            String Another = keyboard.next();
            Another.toLowerCase();

            break;


     case "water":
            WaterSpeed = Distance/Water;
            System.out.print("\nThe time to for sound to travel ");
            System.out.print(Distance);
            System.out.print(" feet through WATER" +"\n");
            System.out.printf("%.6f",WaterSpeed);
            System.out.print(" seconds or ");
            System.out.printf("%.1f", OneFootPerSecond*Water);
            System.out.print(" miles per hour."); 
    break;

     case "steel":
            SteelSpeed = Distance/Steel;
            System.out.print("\nThe time to for sound to travel ");
            System.out.print(Distance);
            System.out.print(" feet through STEEL" +"\n");
            System.out.printf("%.6f",SteelSpeed);
            System.out.print(" seconds or ");
            System.out.printf("%.1f", OneFootPerSecond*Steel);
            System.out.print(" miles per hour."); 
    break;     

          case "earth":
            EarthSpeed = Distance/Water;
            System.out.print("\nThe time to for sound to travel ");
            System.out.print(Distance);
            System.out.print(" feet through EARTH" +"\n");
            System.out.printf("%.6f",EarthSpeed);
            System.out.print(" seconds or ");
            System.out.printf("%.1f", OneFootPerSecond*Earth);
            System.out.print(" miles per hour."); 
    break;
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2 回答 2

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没问题。

我看到以下问题：

Input.toLowerCase();

不工作使用

Input=Input.toLowerCase();

因为该函数只返回一个新字符串

于 2013-09-27T22:56:24.880 回答
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首先，按照评论中的建议，更改Input.toLowerCase();为：

Input = Input.toLowerCase();

或更改switch(Input)为：

switch(Input.toLowerCase())

现在到有趣的部分......

default:添加一个块，而不是一个新单词的大小写。如果没有其他匹配项，这将运行。

switch (Input)

    {

        case "air":
            AirSpeed = Distance/Air;
            System.out.print("\n \nThe time to for sound to travel ");
            System.out.print(Distance);
            System.out.print(" feet through AIR" +"\n");
            System.out.printf("%.6f", AirSpeed);
            System.out.print(" seconds or ");
            System.out.printf("%.1f", OneFootPerSecond*Air);
            System.out.print(" miles per hour."); 
            System.out.print("\n \nEnter Yes for another calculation, else No: ");
            String Another = keyboard.next();
            Another.toLowerCase();
        break;


        // Some more cases...


        default:
            // Something something that will happen as a "last resort".

        break;

  } // End switch
于 2013-09-27T22:49:57.987 回答