Question

基本上我试图让一些while循环检查字符串中的特定索引。验证refNum长度的第一个循环工作正常。当它进入更大的while循环时它只是跳过它而我不确定为什么，任何反馈都会非常感激。

package testing_code;
import java.util.Scanner;

/**
 *
 * @author A.Con
 */
public class Testing_Code
{

    public static void main(String[] args)
    {
        Scanner userInput = new Scanner (System.in);
        String refNum;

        System.out.println("Enter refNum: example - WE123A");
        refNum = userInput.next();

        int rnLength = refNum.length();

        while(rnLength < 6 || rnLength > 6)
        {
           System.out.println("Invalid reference number. Try again.\n ");
           System.out.println("Please enter reference No.:  ");
           refNum = userInput.next();
           rnLength = refNum.length();
        }


        while(!(refNum.charAt(0) >= 'A') && !(refNum.charAt(0) <= 'Z') && !(refNum.charAt(1) >= 'A') && !(refNum.charAt(1) <= 'Z')) 
        { 
            while(!(refNum.charAt(2) >= '0') && !(refNum.charAt(2) <= '9') && !(refNum.charAt(3) >= '0') && !(refNum.charAt(3) <= '9')) 
              {
                  while(!(refNum.charAt(4) >= '0') && !(refNum.charAt(4) <= '9') && !(refNum.charAt(5) >= 'A') && !(refNum.charAt(5) <= 'Z'))
                  {
                System.out.println("Invalid reference number. Try again.\n ");
                System.out.println("Please enter reference No.:  ");
                refNum = userInput.next();                    
                  }
              }
        }

Answer 1

首先!(A >= B)相当于(A < B)。因此!(refNum.charAt(0) >= 'A') && !(refNum.charAt(0) <= 'Z')相当于(refNum.charAt(0) < 'A') && (refNum.charAt(0) > 'Z')。

如果您查看ASCII table，您会看到＆＃34;小于A且大于Z＆＃34;是相互排斥的条件。它们永远不会同时成立，因此while循环最终会简化为while(false)

Answer 2

您的条件while(!refNum.charAt(0) >= 'A') && !(refNum.charAt(0) <= 'Z'))始终为false，因为char不能同时小于'A'且大于'Z'。使用||代替&&，您就可以了。

我建议使用

Character.isLetter(refNum.charAt(0)) // returns true if the passed character is a letter
Character.isDigit(refNum.charAt(0)) // returns true, if the passed character is a digit.

更简单＆amp;易于阅读。

Answer 3

您的while条件都错了。例如!(refNum.charAt(0) >= 'A') && !(refNum.charAt(0) <= 'Z')检查某个字符是否低于A 且高于Z，这是不可能的;你应该使用or代替。

事实上，有一些很多方法可以改善这一点。这是我的版本

public class Testing_Code
{
    static boolean inRange(char c, char first, char last) {
        return (c >= first) && (c <= last);
    }

    public static void main(String[] args)
    {
        Scanner userInput = new Scanner (System.in);
        String refNum;

        System.out.println("Enter refNum: example - WE123A");
        refNum = userInput.next();

        while(refnum.length() != 6 
                || !inRange(refnum.charAt(0), 'A', 'Z') 
                || !inRange(refnum.charAt(1), 'A', 'Z') 
                || !inRange(refnum.charAt(2), '0', '9') 
                || !inRange(refnum.charAt(3), '0', '9') 
                || !inRange(refnum.charAt(4), '0', '9') 
                || !inRange(refnum.charAt(5), 'A', 'Z'))
        {
            System.out.println("Invalid reference number. Try again.\n ");
            System.out.println("Please enter reference No.:  ");
            refNum = userInput.next();
            rnLength = refNum.length();
        }
    }
}

循环java没有正则表达式验证字符串

3 个答案: