當輸入Y/N時不返回錯誤

Question

如果用戶沒有輸入Y/N作爲答案，我該如何返回錯誤並再次詢問Do you want to try again (Y/N)?？

import java.io.*; 

public class Num10 { 
    public static void main(String[] args){ 
     String in=""; 
     int start=0, end=0, step=0; 

     BufferedReader input = new BufferedReader(new InputStreamReader(System.in)); 

     do{ 
      try{ 
       System.out.print("Input START value = "); 
       in=input.readLine(); 
       start=Integer.parseInt(in); 
       System.out.print("Input END value = "); 
       in=input.readLine(); 
       end=Integer.parseInt(in); 
       System.out.print("Input STEP value = "); 
       in=input.readLine(); 
       step=Integer.parseInt(in); 
      }catch(IOException e){ 
       System.out.println("Error!"); 
      } 

      if(start>=end){ 
       System.out.println("The starting number should be lesser than the ending number"); 
       System.exit(0); 
      }else 
      if(step<=0){ 
       System.out.println("The step number should always be greater than zero."); 
       System.exit(0); 
      } 

      for(start=start;start<=end;start=start+step){ 
       System.out.println(start); 
      } 

      try{ 
       System.out.print("\nDo you want to try again (Y/N)?"); 
       in=input.readLine(); 
      }catch(IOException e){ 
       System.out.println("Error!"); 
      } 
     }while(in.equalsIgnoreCase("Y")); 

    } 
} 

我應該使用if-else？

Answer 1

首先+1供給完全編譯程序。這是問題提出者超過90％的問題。 在最終try/catch塊，檢查用戶輸入「Y」或「N」這樣

 try{ 
      while (!in.equalsIgnoreCase("y") && !in.equalsIgnoreCase("n")) { 
        System.out.print("\nDo you want to try again (Y/N)?"); 
        in=input.readLine(); 
      } 
     }catch(IOException e){ 
      System.out.println("Error!"); 
     } 
    }while(in.equalsIgnoreCase("Y")); 

Answer 2

做這樣的事情：

BufferedReader input = new BufferedReader(new InputStreamReader(System.in)); 
boolean w4f = true; 

do { 
    String in = input.readLine(); 

    if ("Y".equalsIgnoreCase(in)) { 
     w4f = false; 

     // do something 

    } else if ("N".equalsIgnoreCase(in)) { 
     w4f = false; 

     // do something 

    } else { 

     // Your error message here 
     System.out.println("blahblah"); 
    } 

} while(w4f);