使用開關並嘗試聲明來驗證用戶輸入

Question

我一直在這一點工作，它不會編譯。它給了我一個錯誤說

變量的選擇可能沒有 初始化 開關（選擇） ^

，但我在程序變量集。所以我不知道問題是什麼？它是否真的能夠避免編譯？

import java.io.*; 
    import javax.swing.JOptionPane; 

    public class MyType 
    { 
     public static void main(String[] args) 
     { 
      String strChoice = "", strTryString, strTryInt, strTryDouble; 
      Integer choice, tryInt; 
      double tryDouble; 
      boolean done = false; 

      while(!done) 
     { 
       try 
       { 
        String answer = JOptionPane.showInputDialog(null, "What's my type\n\n\n1) String\n2) integer\n3) double\n4) Quit the program"); 
        choice = Integer.parseInt(strChoice); 

        //test for valid codes 1, 2, 3, or 4 
        if (choice<1 || choice>4) throw new NumberFormatException(); 
        else done = true; 
       } 
        catch(NumberFormatException e) 
       { 
        JOptionPane.showInputDialog(null, "Please enter a 1, 2, 3, or 4", "Error", JOptionPane.INFORMATION_MESSAGE); 
        switch(choice) 
       { 
         case 1: 
          JOptionPane.showMessageDialog(null, "Correct, any input can be saved as a String"); 
          break; 

         case 2: 
          JOptionPane.showMessageDialog(null, "Correct!"); 
          tryInt = Integer.parseInt(strChoice); 
          break; 

         case 3: 
          JOptionPane.showMessageDialog(null, "Correct!"); 
          tryDouble = Integer.parseInt(strChoice); 
          break; 

         case 4: 
          done = true; 
          JOptionPane.showMessageDialog(null, "Exit."); 
          System.exit(0); 
          break; 
         default: throw new NumberFormatException(); 
      } 
      } 

      } 
     } 
    } 

Answer 1

如果showInputDialog拋出，那麼'choice'沒有設置。

try 
      { 
       String answer = JOptionPane.showInputDialog(null, "What's my type\n\n\n1) String\n2) integer\n3) double\n4) Quit the program"); 
       choice = Integer.parseInt(strChoice); 

       //test for valid codes 1, 2, 3, or 4 
       if (choice<1 || choice>4) throw new NumberFormatException(); 
       else done = true; 
      } 
       catch(NumberFormatException e) 
      { 

Answer 2

你應該嘗試塊之前iniatialize選擇的變量，因爲你是在抓，在某些情況下，如果異常被選擇happining那麼varaible選擇將未初始化的初始化之前扔引用它。