Question

我试图让程序根据卡号的第一位数字在屏幕上打印卡片类型。该程序编译正常并运行，但它不会将卡类型语句放在屏幕上。我确信这只是一个简单的修复，但我花了几个小时试图发现它可能是什么。我在这里缺少什么？

public static void main (String [] args ) {


    System.out.println ( "Please enter your credit card number without spaces." );
    Scanner keyIn = new Scanner ( System.in );

    long ccNum = keyIn.nextLong ();
    String cNum = ccNum + "";    


    switch ( cNum.charAt ( 0 ) )
      {
        case 4:
            System.out.println ( "The card is a Visa" );
            break;

        case 5:
            System.out.println ( "The card is a MasterCard" );
            break;

        case 6:
            System.out.println ( "The card is a Discover Card" );
            break;

        case 37:
            System.out.println ( "The card is an American Express Card" );
            break;
      }
}

Answer 1

public static void main (String [] args ) { System.out.println ( "Please enter your credit card number without spaces." ); Scanner keyIn = new Scanner ( System.in ); long ccNum = keyIn.nextLong (); String cNum = ccNum + ""; switch ( Character.getNumericValue(cNum.charAt ( 0 )) ) { case 4: System.out.println ( "The card is a Visa" ); break; case 5: System.out.println ( "The card is a MasterCard" ); break; case 6: System.out.println ( "The card is a Discover Card" ); break; case 37: System.out.println ( "The card is an American Express Card" ); break; } }返回charAt，您将其与其面值所代表的int进行比较。即，不应使用char，4和5，而应使用6，'4'和'5'。另请注意，“37”是两个字符，因此您不能只评估第一个字符。相反，您可以使用String.startsWith(String)和一系列if-else条件：

'6'

Answer 2

您正在将char与整数进行比较。

使用switch语句查看解决方案：

public static void main (String [] args ) {

    System.out.println("Please enter your credit card number without spaces.");
    final Scanner keyIn = new Scanner(System.in);

    long ccNum = 0L;

    if (keyIn.hasNext()) {
      ccNum = keyIn.nextLong(); 
    }

    final String cNum = "" + ccNum;

    int firstDigits = Integer.parseInt(cNum.substring(0, 2));

    if (firstDigits > 37) {
      firstDigits /= 10;
    }

    switch(firstDigits) {
        case 4: {
          System.out.println("The card is a Visa");
          break;
        }
        case 5: {
          System.out.println("The card is a MasterCard");
          break;
        }
        case 6: {
          System.out.println("The card is a Discover Card");
          break;
        }
        case 37: {
          System.out.println("The card is an American Express Card");
          break;
        }
        default: {
          System.out.println("Incorrect card number");
        }
    }
}

Answer 3

如果您想将卡号与您的案例进行比较。您需要将var elemetsWithClassClose = document.getElementsByClassName("close"); var contactSpan = elemetsWithClassClose[0];转换为cNum.charAt ( 0 ) )。但是案例37 ??

呢？

int

案例陈述代码不会显示在屏幕上，但符合条件且没有错误

3 个答案: