用另一个具有相同char索引的字符串替换另一个字符串中的字符

Question

I'm trying to search and reveal unknown characters in a string. Both strings are of length 12.

Example:

     String s1 = "1x11222xx333";
     String s2 = "111122223333"

The program should check for all unknowns in s1 represented by x|X and get the relevant chars in s2 and replace the x|X by the relevant char.

So far my code has replaced only the first x|X with the relevant char from s2 but printed duplicates for the rest of the unknowns with the char for the first x|X.

Here is my code:

    String VoucherNumber = "1111x22xx333";
    String VoucherRecord = "111122223333";
    String testVoucher = null;
    char x = 'x'|'X';

    System.out.println(VoucherNumber); // including unknowns


            //find x|X in the string VoucherNumber
            for(int i = 0; i < VoucherNumber.length(); i++){

                   if (VoucherNumber.charAt(i) == x){

                       testVoucher = VoucherNumber.replace(VoucherNumber.charAt(i), VoucherRecord.charAt(i));

                   }


            }

                     System.out.println(testVoucher); //after replacing unknowns
        }


    }

Answer 1

I am always a fan of using StringBuilder s, so here's a solution using that:

private static String replaceUnknownChars(String strWithUnknownChars, String fullStr) {
    StringBuilder sb = new StringBuilder(strWithUnknownChars);
    while ((int index = Math.max(sb.toString().indexOf('x'), sb.toString().indexOf('X'))) != -1) {
        sb.setCharAt(index, fullStr.charAt(index));
    }

    return sb.toString();
}

It's quite straightforward. You create a new string builder. While a x or X can still be found in the string builder ( indexOf('X') != -1 ), get the index and setCharAt .

Answer 2

Your are using String.replace(char, char) the wrong way, the doc says

Returns a new string resulting from replacing all occurrences of oldChar in this string with newChar.

So you if you have more than one character, this will replace every one with the same value.

You need to "change" only the character at a specific spot, for this, the easiest is to use the char array that you can get with String.toCharArray , from this, this is you can use the same logic.

Of course, you can use String.indexOf to find the index of a specific character

Note : char c = 'x'|'X' ; will not give you the expected result. This will do a binary operation giving a value that is not the one you want.

The OR will return 1 if one of the bit is 1.

0111 1000 (x)
0101 1000 (X)
OR
0111 1000 (x)

But the result will be an integer (every numeric operation return at minimum an integer, you can find more information about that)

You have two solution here, you either use two variable (or an array) or if you can, you use String.toLowerCase an use only char c = 'x'