Removing extra spaces without using a regular expression

Question

I want to remove the extra spaces without using a regular expression. I'm using two while loops.

How can this become better / more elegant?

String str = "Hola caracola ";
char[] src = str.toCharArray(), dest = new char[src.length];
int i = 0, j = 0;
while (i < src.length - 1) {
 while (i < src.length - 1 && src[i] == ' ' && src[i + 1] == ' ') {
 i++;
 }
 dest[j++] = src[i++];
}
System.out.println(new String(dest, 0, j));

• Mathieu Guindon: I'd start by making it into a proper function I guess. Right?

Answer 1

Your code is buggy: it fails to copy the last character.

As @Mat'sMug says, defining a function would be a good idea.

The task can be done with one array and one loop.

public static String compressConsecutiveSpaces(String str) {
 if (str.isEmpty()) return str;
 char[] chars = str.toCharArray();
 int dest = 1;
 for (int src = 1; src < chars.length; src++) {
 if (!(chars[src - 1] == ' ' && chars[src] == ' ')) {
 chars[dest++] = chars[src];
 }
 }
 return new String(chars, 0, dest);
}

Answer 2

I just took the OCA for Java 7SE and there were a lot of questions about StringBuilder, so using that was my first inclination. The answer using a char array might be quicker, but the code below seems pretty clear and straightforward as an alternative.

public static String removeDoubleSpaces(String str)
{
 StringBuilder sb = new StringBuilder(str);
 int dblSpaceLoc;
 while (0 <= dblSpaceLoc = sb.indexOf(" "))
 {
 sb.deleteCharAt(dblSpaceLoc);
 }
 // if also wish to remove leading/trailing spaces:
 // return sb.toString().trim(); 
 return sb.toString();
}

• 200_success: Note that StringBuilder.deleteCharAt() would cause all of the subsequent characters to be immediately copied over to fill the gap. For long strings, doing multiple .deleteCharAt() operations would be a performance problem.
• Phil Freihofner: Yes, deleteCharAt() make use of system.arraycopy.