允許Java識別不等於想要的值的輸入

Question

我是Java和本站的新手，所以請對我犯的任何錯誤留下憐憫之心，我在我的智慧結尾！

我想製作一個程序，通過不同的媒介來計算聲音的速度。截至目前，該程序將要求用戶輸入距離並允許輸入，對於媒體也是如此。我創建了幾個案例來計算正確工作的給定介質的答案。

問題是，當我嘗試創建一個循環來識別媒體輸入是否不是可用的4個選項之一。我能夠成功地創建一個循環，以識別距離輸入是否不是數值，並嘗試使用類似的原則來處理媒體輸入，但要麼一直處於無限循環中，要麼在我輸入時出現錯誤條目時創建的消息正確的選擇。 我已經嘗試了我曾經教過的基本循環：for，do-while等等，但我被卡住了。任何和所有的建議表示讚賞，非常感謝你！

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; 

Answer 1

首先，如評論所說，改變Input.toLowerCase();喜歡的東西：

Input = Input.toLowerCase(); 

或更改switch(Input)到：

switch(Input.toLowerCase()) 

現在到了有趣的部分...

而不是一個新單詞的情況下，添加一個default: b鎖。這將運行，如果沒有其他任何匹配。

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 

Answer 2

沒問題。

我看到下面的問題：

Input.toLowerCase();

工作不使用

Input=Input.toLowerCase();

因爲函數只返回一個新的String