输入字符串而不是整数（Java）

Question

我是一个绝对的初学者，没有任何编程语言的经验。

我写了一个程序作为将阿拉伯数字转换成罗马数字的练习。有用。不过，如果输入字符串而不是整数，我想添加一个用于处理问题的部分。不知道如何做到这一点。我试图使用try/catch，但我不知道如何正确使用它。现在程序要我两次输入一个数字。该怎么办？

这里是他的主要方法：

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

您的控制机制是真实的，但只能使用一次。你必须把它放在一个循环中，以便它可以允许用户最后输入一个整数。

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()方法来检查。

如果此扫描器输入中的下一个标记可被解释为int值，则此方法返回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，这将覆盖所有这一切都没有Integer的投入，不仅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

试试这个：

 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

试试这个，

你需要先初始化numArabic一些价值。

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

你输入什么程序是从语法错误和逻辑errors.But免费问只有一次进入整数值只是重写代码following.We在捕捉附着第二SOP功能block.So如果输入不匹配，它会要求再次输入。 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(); 
     }