使用递归从字符串的某个索引处替换字符

Question

Hi im trying to create a method to remove the spaces from a word recursively. Ive done this so far, and im really not sure why its not working.

public static String compact (String line)
{

    for (int x = 0 ; x < line.length () ; x++)
    {
        if (line.charAt (x) == ' ')
        {
            String newLine = line.substring (0, x) + line.substring (x);
            return compact (newLine);
        }
        else
            break;
    }
    return line;
}

This just returns the original string without removing any spaces. Can someone please tell me what im doing wrong, thanks.

Answer 1

Just remove the

else break;  

part, because if the first character of your String is not a whitespace, the loop will terminate

Also replace

String newLine = line.substring (0, x) + line.substring (x);

with

String newLine = line.substring (0, x) + line.substring (x + 1);

because you are actually not removing the whitespace, but copying the whole string over and over again. This is why you get a StackOverflowError .

---

The method should look like this:

public static String compact(String line) {
    for (int x = 0; x < line.length(); x++) {
        if (line.charAt(x) == ' ') {
            String newLine = line.substring (0, x) + line.substring (x+1);
            return compact(newLine);
        }
    }
    return line;
}

Answer 2

You can get rid of the for loop and fix that in one line of code...

Just use..

  //changes a string "moon shine" to "moonshine"
  String newLine = line.trim().replaceAll(" +", "");
  System.out.println(newLine);