輸入字符串而不是整數（Java）

Question

我是一個絕對的初學者，沒有任何編程語言的經驗。

我寫了一個程序作爲將阿拉伯數字轉換成羅馬數字的練習。有用。不過，如果輸入字符串而不是整數，我想添加一個用於處理問題的部分。不知道如何做到這一點。我試圖使用try/catch，但我不知道如何正確使用它。現在程序要我兩次輸入一個數字。該怎麼辦？

這裏是他的主要方法：

public static void main(String[] args) { 

    int numArabic; 
    boolean validEntry; 

    try { 
      System.out.println("Enter an integer number between 1 and 3999!"); 
      Scanner scan = new Scanner(System.in); 
      numArabic = scan.nextInt(); 
      validEntry = true; 
     } catch (InputMismatchException e) { 
      System.out.println("Entered value is not an integer!"); 
     } 

    System.out.println("Enter an integer number between 1 and 3999!"); 
    Scanner scan = new Scanner(System.in); 
    numArabic = scan.nextInt();        

    if ((numArabic < 1) || (numArabic > 3999)) { 
      System.out.println(); 
      System.out.print("Wrong number. "); 
      System.out.print("Enter an integer number between 1 and 3999!"); 
      System.out.println(); 
      } 
    else { 
      String numRoman1 = toRomanOne(numArabic % 10); 
      String numRoman2 = toRomanTwo(((numArabic/10) % 10)); 
      String numRoman3 = toRomanThree(((numArabic/100) % 10)); 
      String numRoman4 = toRomanFour(numArabic/1000); 
      System.out.print("The number " + numArabic + " is equal to: "); 
      System.out.print(numRoman4+numRoman3+numRoman2+numRoman1 + "."); 
    } 
} 

Answer 1

您的控制機制是真實的，但只能使用一次。你必須把它放在一個循環中，以便它可以允許用戶最後輸入一個整數。

boolean validEntry; 

do { 
    try { 
     System.out.println("Enter an integer number between 1 and 3999!"); 
     Scanner scan = new Scanner(System.in); 
     numArabic = scan.nextInt(); 
     validEntry = true; 
    } 
    catch (InputMismatchException e) { 
     validEntry = false; 
     System.out.println("Entered value is not an integer!"); 
    } 
} 
while(!validEntry); 

Answer 2

您可以使用Scanner#hasNextInt()方法來檢查。

如果此掃描器輸入中的下一個標記可被解釋爲int值，則此方法返回true。

if (scan.hasNextInt()) { 
    // Do the process with Integer. 
} else { 
    // Do the process if it is not an Integer. 
} 

需要注意的是，這將覆蓋所有這一切都沒有Integer的投入，不僅String。

Answer 3

public static void main(String[] args) { 

    int numArabic; 
    boolean validEntry = false; 

    while (validEntry = false){ 
    try { 

      System.out.println("Enter an integer number between 1 and 3999!"); 
      Scanner scan = new Scanner(System.in); 
      numArabic = scan.nextInt(); 
      validEntry = true; 
     } 

     catch (InputMismatchException e) { 
      System.out.println("Entered value is not an integer!"); 
      validEntry = false; 
     } 
    }     

    if ((numArabic < 1) || (numArabic > 3999)) { 
      System.out.println(); 
      System.out.print("Wrong number. "); 
      System.out.print("Enter an integer number between 1 and 3999!"); 
      System.out.println(); 
      } 
    else { 
      String numRoman1 = toRomanOne(numArabic % 10); 
      String numRoman2 = toRomanTwo(((numArabic/10) % 10)); 
      String numRoman3 = toRomanThree(((numArabic/100) % 10)); 
      String numRoman4 = toRomanFour(numArabic/1000); 
      System.out.print("The number " + numArabic + " is equal to: "); 
      System.out.print(numRoman4+numRoman3+numRoman2+numRoman1 + "."); 
    } 
} 

Answer 4

試試這個：

 boolean b=true; 
    while(b) 
    { 
     try 
     { 
     System.out.println("Enter an integer number between 1 and 3999!"); 
     Scanner scan = new Scanner(System.in); 
     numArabic = scan.nextInt(); 
     validEntry = true; 
     } 
     catch (InputMismatchException e) 
     { 
      System.out.println("Entered value is not an integer!"); 

     } 
     if(validEntry) 
     { 
     if ((numArabic < 1) || (numArabic > 3999)) 
     { 
     System.out.println(); 
     System.out.print("Wrong number. "); 
     System.out.print("Enter an integer number between 1 and 3999!"); 
     System.out.println(); 
     } 
     else 
     { 
     String numRoman1 = toRomanOne(numArabic % 10); 
     String numRoman2 = toRomanTwo(((numArabic/10) % 10)); 
     String numRoman3 = toRomanThree(((numArabic/100) % 10)); 
     String numRoman4 = toRomanFour(numArabic/1000); 
     System.out.print("The number " + numArabic + " is equal to: "); 
     System.out.print(numRoman4+numRoman3+numRoman2+numRoman1 + "."); 
     } 
     b=false; 
    }//end of if 
}//end of while 

Answer 5

試試這個，

你需要先初始化numArabic一些價值。

public static void main(String[] args) { 
    int numArabic = 0; 
    boolean validEntry; 

    try { 
     System.out.println("Enter an integer number between 1 and 3999!"); 
     Scanner scan = new Scanner(System.in); 
     numArabic = scan.nextInt(); 
     validEntry = true; 
    } 

    catch (InputMismatchException e) { 
     System.out.println("Entered value is not an integer!"); 
    } 


    if ((numArabic < 1) || (numArabic > 3999)) { 

    } else { 

    } 

} 

Answer 6

你輸入什麼程序是從語法錯誤和邏輯errors.But免費問只有一次進入整數值只是重寫代碼following.We在捕捉附着第二SOP功能block.So如果輸入不匹配，它會要求再次輸入。 public static void main（String [] args）{

int numArabic; 
    boolean validEntry; 

    try { 
      System.out.println("Enter an integer number between 1 and 3999!"); 
      Scanner scan = new Scanner(System.in); 
      numArabic = scan.nextInt(); 
      validEntry = true; 
     } catch (InputMismatchException e) { 
      System.out.println("Entered value is not an integer!"); 


System.out.println("Enter an integer number between 1 and 3999!"); 
     Scanner scan = new Scanner(System.in); 
     numArabic = scan.nextInt(); 
     }