抛出异常，即使数据类型正确

Question

我已经构建了一个货币转换程序，并且需要用户输入。在该计划的某一点，我要求他们想要兑换的货币。但是，没有任何东西阻止他们将“java”作为货币或任何其他词汇。

这里是我当前的代码，我会解释多一点什么我在寻找进一步下跌：

import java.util.Scanner; 

public class Exchange { 
    public static void main(String[] args) { 
     int i = 1; 
     Scanner inn = new Scanner(System.in); 
     try{ 
      while (i > 0){ 
       double USDrate = 0.12808; 
       double EURrate = 0.107643821; 
       double GBPrate = 0.098872935; 
       System.out.println("Hello, what currency would you like to convert to?"); 
       System.out.println("Types: USD/EUR/GBP"); 
       String type = inn.nextLine(); 
       System.out.println("Hello, how much would you like to convert?"); 
       double NOK = inn.nextDouble(); 
       if(type.equalsIgnoreCase("USD")){ 
         System.out.printf(NOK + "kr equals $%.2f \n", (NOK*USDrate)); 
       }else if(type.equalsIgnoreCase("EUR")){ 
         System.out.printf(NOK + "kr equals €%.2f \n", (NOK*EURrate)); 
       }else if(type.equalsIgnoreCase("GBP")){ 
         System.out.printf(NOK + "kr equals £%.2f \n", (NOK*GBPrate)); 
       }else { 
        // This is where I would like to throw an exception if what they put in doesn't make sense. 
       } 
       inn.nextLine(); 
       System.out.println("Would you like to convert more?"); 
       System.out.println(" YES/NO "); 
       String ans = inn.nextLine(); 
       if(ans.equalsIgnoreCase("NO")){ 
         i = 0; 
       } 
      } 
     } 
     catch(Exception e){ 
      System.out.println("You've entered an incorrect value! Restart."); 
     } 
    } 
} 

我想除了采取while -loop内的最后else语句来下进行，正如你所看到的，我有一个评论，那就是那个意思。我还想在代码块中有同样的例外，我问他们是否想要转换更多。

任何人都可以提供帮助吗？如果您需要的任何细节丢失，我会根据要求给他们。

在此先感谢。

我想出了如何使它成为我想要的方式。也不例外必要的，但这里是我的解决方案：

import java.util.Scanner; 

public class Exchange { 
    public static void main(String[] args) { 
     int i = 1; 
     Scanner inn = new Scanner(System.in); 
     try{ 
      while (i > 0){ 
       double USDrate = 0.12808; 
       double EURrate = 0.107643821; 
       double GBPrate = 0.098872935; 
       System.out.println("Hello, what currency would you like to convert to?"); 
       System.out.println("Types: USD/EUR/GBP"); 
       String type = inn.nextLine(); 
       if(!type.equalsIgnoreCase("USD") && !type.equalsIgnoreCase("EUR") && !type.equalsIgnoreCase("GBP")){ 
        System.out.println("Not available currency! Try again."); 
        break; 
       } 
       System.out.println("How much would you like to convert?"); 
       double NOK = inn.nextDouble(); 
       if(type.equalsIgnoreCase("USD")){ 
         System.out.printf(NOK + "kr equals $%.2f \n", (NOK*USDrate)); 
       }else if(type.equalsIgnoreCase("EUR")){ 
         System.out.printf(NOK + "kr equals €%.2f \n", (NOK*EURrate)); 
       }else if(type.equalsIgnoreCase("GBP")){ 
         System.out.printf(NOK + "kr equals £%.2f \n", (NOK*GBPrate)); 
       } 
       inn.nextLine(); 
       System.out.println("Would you like to convert more?"); 
       System.out.println(" YES/NO "); 
       String ans = inn.nextLine(); 
       if(ans.equalsIgnoreCase("NO")){ 
         i = 0; 
       } 
      } 
     } 
     catch(Exception e){ 
      System.out.println("You've entered an incorrect value! Restart."); 
     } 
    } 
} 

使用的另一种方法:)感谢您的答案不管怎么说，他们帮了不少忙。

Answer 1

而不是使用if/else if... block我建议使用switch语句。在默认情况下，你可以抛出一个异常。因为你赶上Exception只是让throw new Exception();

  type = type.toUpperCase(); 
      switch(type) { 
       case "USD": 
        System.out.printf(NOK + "kr equals $%.2f \n", (NOK*USDrate)); 
       break; 

       case "EUR": 
        System.out.printf(NOK + "kr equals €%.2f \n", (NOK*EURrate)); 
       break; 

       case "GBP": 
        System.out.printf(NOK + "kr equals £%.2f \n", (NOK*GBPrate)); 
       break; 

       default: 
        throw new Exception(); 
      } 

而且不要忘记关闭扫描仪

 finally { 
      inn.close(); 
     } 

Answer 2

为什么你想在这里抛出异常！

在else块

System.out.println("You've entered an incorrect value! Please provide correct value"); // something similar. 

只是打印一些有意义的信息。如果你真的想抛出异常，然后写在下面else块的代码。

throw new Exception(); 

Answer 3

import java.util.Scanner; 

public class Exchange { 
    public static void main(String[] args) throws Exception { 
     int i = 1; 
     Scanner inn = new Scanner(System.in); 
     while (i > 0) { 
      double USDrate = 0.12808; 
      double EURrate = 0.107643821; 
      double GBPrate = 0.098872935; 
      System.out.println("Hello, what currency would you like to convert to?"); 
      System.out.println("Types: USD/EUR/GBP"); 
      String type = inn.nextLine(); 
      System.out.println("Hello, how much would you like to convert?"); 
      double NOK = inn.nextDouble(); 
      if (type.equalsIgnoreCase("USD")) { 
       System.out.printf(NOK + "kr equals $%.2f \n", (NOK * USDrate)); 
      } else if (type.equalsIgnoreCase("EUR")) { 
       System.out.printf(NOK + "kr equals €%.2f \n", (NOK * EURrate)); 
      } else if (type.equalsIgnoreCase("GBP")) { 
       System.out.printf(NOK + "kr equals £%.2f \n", (NOK * GBPrate)); 
      } else { 
       throw new Exception(); 
      } 
      inn.nextLine(); 
      System.out.println("Would you like to convert more?"); 
      System.out.println(" YES/NO "); 
      String ans = inn.nextLine(); 
      if (ans.equalsIgnoreCase("NO")) { 
       i = 0; 
      } 
     } 
    } 
     /*(Exception e) { 
      System.out.println("You've entered an incorrect value! Restart.");*/ 
} 

它会扔在别的part.In代码其他部分的异常将无法正常工作，有一个例外，它会直接转到catch块。