如何检查特定索引处的字符是否与数组中的项目匹配

Question

I'm trying to take a string as an input (around 5 - 7 characters), iterate through each character and check whether or not it matches a character from an array. For example:

static String Registration(String reg) {
    int[] numbers = {0, 1, 2, 3, 4, 5, 6, 7 , 8, 9,};
    if (reg.length() >= 7) {
        for (int i = 0; i < reg.length(); i++) {
            reg.indexOf(numbers[i]);
        }
    }
}

The above is clearly wrong. However, I hope it illustrates what I'm trying to do. For example, if the string was "H3llo", I would want to check each character in the string and see if it matches with any items in the array. If it does, I would like to store the index as an int.

This is probably not an efficient way of doing it, but it's the only way I can think of with my current level of learning.

Answer 1

there are several problems with your code here:

• your numbers array is of type int, however you want to compare the characters. use char[] instead and use chars in your array instead of ints like this: '0', '1', ...
• indexOf is not a existing method for arrays, instead use a for loop to iterate through all the entries of the array and compare them by hand
• your function claims to return a String public String Registration but you want to return an int. change this to public int Registration .
• You have no return in your function. you have to use the keyword return in your function if your function should return something.

A possible solution may look like this:

public static int Registration(String reg) {
  char[] numbers = {'0', '1', '2', '3', '4', '5', '6', '7' , '8', '9',}; // use a char array char[] and add numbers as chars to array.
  if (reg.length() >= 7) {
    for (int i = 0; i < reg.length(); i++) {
      char character = reg.charAt(i);
      for(char number : numbers)
      {
        if(number == character)
        {
          return i; // found a matching character, return the index of the matching character
        }
      }
    }
  }
  // return -1 for the case that we find nothing.
  return -1;
}

please try to understand what happens here and do not just copy and paste the solution.

Note: the thing you wish to do can be easily implemented with RegEx, however, this may be too hard for you at your current stage.