如何在java中嘗試並捕獲異常處理後恢復代碼

Question

我實際上遇到了我的程序問題。其實我在學校學習（11年級 - 大專），所以請用非常簡單的語言來解釋我。我正在開發一個測驗，非常基礎的學校項目，所以程序就這樣繼續下去......我希望用戶通過輸入1-4的數字輸入他/她的選擇。我不希望用戶輸入字母，字母或特殊字符或任何其他編號。除了1-4之外。我嘗試使用try和catch，但是我的程序在拋出異常後停止。即使在顯示錯誤信息System.out.println（「輸入無效，請在1-4之間輸入一個數字」）之後，我想讓程序代碼運行。 示例程序

import java.io.*; 
    import java.lang; 
    public class 
    { 
    public static void main()throws IOException 
    { 
    InputStreamReader read =new InputStreamReader (System.in); 
    BufferedReader in =new BufferedReader (read); 
    System.out.println(" Select your category"); 
    System.out.println(" 1. Food"); 
    System.out.println(" 2. National"); 
    System.out.println(""); 
    System.out.println(" Enter your choice"); 
    int choice=Integer.parseInt(in.readLine()); 
    if(choice==1)//food category 
    { 
     int score = 0; 
     System.out.println("what are dynamites made?"); 
     System.out.println("1. peanuts");System.out.println("2. grapes"); 
     System.out.println("3. flaxseeds");System.out.println("4. fish"); 
     System.out.println(" Enter your choice"); 
     int food1= Integer.parseInt(in.readline()); 
     if(c1=1) 
     { System.out.println(" Correct answer"); 
     score=score+10 
     } 
     else 
     { 
     System.out.println(" Wronge answer"); 
     score=score+0 
     } 
     //then i have the second question with the same format 
    } 
     if(choice==2)//natioanl category with the same format as above 
     {//two question with if else statements in them } 
    } 
}// also help me where to add the try and catch statements 

Answer 1

這是對此問題的更優雅的解決方案。沒有嘗試涉及。

import java.io.*; 
    import java.lang; 
    public class 
    { 
    //Compares response to the string representations of all numbers between 1 and numOptions, inclusive. 
    //Returns the matching integer or -1 otherwise. 
    public static int parseResponse(String response, int numOptions) 
    { 
      for(int i=1;i<=numOptions;i++) { 
       if(response.equals(Integer.toString(i))) return i; 
      } 
      return -1; 
    } 

    public static void main()throws IOException 
    { 
     InputStreamReader read =new InputStreamReader (System.in); 
     BufferedReader in =new BufferedReader (read); 
     System.out.println(" Select your category"); 
     System.out.println(" 1. Food"); 
     System.out.println(" 2. National"); 
     System.out.println(""); 
     System.out.println(" Enter your choice"); 

     //New code 
     int choice=-1; 
     while(choice==-1) { 
      choice=parseResponse(in.readLine(),2); 
      if(choice==-1) 
      { 
       System.out.println(" Invalid input. Please enter a number between 1-2"); 
      } 
     } 


     if(choice==1)//food category 
     { 
      int score = 0; 
      System.out.println("what are dynamites made?"); 
      System.out.println("1. peanuts");System.out.println("2. grapes"); 
      System.out.println("3. flaxseeds");System.out.println("4. fish"); 
      System.out.println(" Enter your choice"); 

      //New code 
      int food1=-1; 
      while(food1==-1) { 
       food1=parseResponse(in.readLine(),4); 
       if(food1==-1) 
       { 
        System.out.println(" Invalid input. Please enter a number between 1-4"); 
       } 
      } 

      if(food1==1) 
      { System.out.println(" Correct answer"); 
       score=score+10 
      } 
      else 
      { 
       System.out.println(" Wronge answer"); 
       score=score+0 
      } 
      //then i have the second question with the same format 
     } 
     if(choice==2)//natioanl category with the same format as above 
     {//two question with if else statements in them 
     } 
    } 
}// also help me where to add the try and catch statements 

如果你不知道：

if(response.equals(Integer.toString(i))) return i; 

相同

if(response.equals(Integer.toString(i))) 
{ 
     return i; 
} 

Answer 2

嘿這裏是你可以運行的代碼。

import java.io.*; 

import java.lang.*; 

public class TestTryCatch 
{ 

public static void main(String args[]) 
{ 
    try 
    { 
     InputStreamReader read =new InputStreamReader (System.in); 
     BufferedReader in =new BufferedReader (read); 
     System.out.println(" Select your category"); 
     System.out.println(" 1. Food"); 
     System.out.println(" 2. National"); 
     System.out.println(""); 
     System.out.println(" Enter your choice"); 
     int choice=0; 
     try 
     { 
      choice = Integer.parseInt(in.readLine()); 
     } 
     catch(Exception e) 
     { 
      choice=0; 
     } 
     if(choice==0) 
     { 
      System.out.println("Invalid Input");   
     } 
     if(choice==1)//food category 
     { 
      int score = 0; 
      System.out.println("what are dynamites made?"); 
      System.out.println("1. peanuts");System.out.println("2. grapes"); 
      System.out.println("3. flaxseeds");System.out.println("4. fish"); 
      System.out.println(" Enter your choice"); 
      int food1= Integer.parseInt(in.readLine()); 
      if(food1==1) 
      { System.out.println(" Correct answer"); 
      score=score+10; 
      } 
      else 
      { 
       System.out.println(" Wronge answer"); 
       score=score+0; 
      } 

     } 
     if(choice==2) 
     { 
     } 
    } 
    catch(Exception e) 
    { 
     e.printStackTrace(); 
    } 
} 
} 

把你嘗試轉換成整型。如果你的代碼給出了異常，它會進入異常塊並處理任何你想要的值。在這裏，我把它作爲0，你也可以分配-1。

如果此代碼有幫助還原，請回復。

Answer 3

程序發生崩潰的地方就在這裏：

int food1= Integer.parseInt(in.readline()); 
if(c1=1) 
{ System.out.println(" Correct answer"); 
    score=score+10 
} 

「C1」不是一個定義的變量，所以使用它會導致程序，無論用戶輸入什麼崩潰。您應該將「c1」替換爲「food1」。此外，賦值運算符「=」應替換爲比較運算符「==」。

退房整數的Javadoc（谷歌「整型的javadoc」），你會發現，

public static int parseInt(String s) 
       throws NumberFormatException 

那麼NumberFormatException的是我們需要趕上。在運行程序時，您還可以通過查看堆棧跟蹤來找出拋出的異常和位置。

每當引發異常時，錯誤之後和下一個'}'之前的所有內容都會被跳過。由於大部分代碼應該在錯誤發生後執行很好，我們要保持我們的try-catch小，即

try { 
    int choice=Integer.parseInt(in.readLine()); 
} catch (NumberFormatException ex) { 
    //Not a number 
} 

我們需要的變量，「選擇」是我們嘗試的訪問之外，讓我們拭目以待在我們的嘗試之外聲明它。

int choice; 

try { 
    choice=Integer.parseInt(in.readLine()); 
} catch (NumberFormatException ex) { 
    //Not a number 
} 

但是，NumberFormatException不會告訴您用戶是否輸入了除1-4之外的數字。所以你必須添加你自己的驗證。

int choice; 

try { 
    choice=Integer.parseInt(in.readLine()); 
    if(choice<1 || choice>4) ; //Not 1-4 
} catch (NumberFormatException ex) { 
    //Not a number 
} 

最後，我們需要跟蹤我們的輸入是否有效，並在需要時循環。

boolean valid=false; 

while(!valid) { 

    int choice; 

    try { 
     choice=Integer.parseInt(in.readLine()); 
     if(choice<1 || choice>4) valid=false; //Not 1-4 
     else valid=true; 
    } catch (NumberFormatException ex) { 
     //Not a number 
     valid=false; 
    } 

    if(valid) { 
     //Handle valid response here 
    } else { 
     System.out.println(" Invalid input. Please enter a number between 1-4"); 
    } 
} 

祝你好運！