How to trim the whitespace from a string? [duplicate]

Question

I am writing this function for a J2ME application, so I don't have some of the more advanced / modern Java classes available to me. I am getting java.lang.ArrayIndexOutOfBoundsException on this. So, apparently either it doesn't like the way I've initialized the newChars array, or I'm not doing something correctly when calling System.arraycopy.

/*
 * remove any leading and trailing spaces
 */
public static String trim(String str) {
    char[] chars = str.toCharArray();
    int len = chars.length;
    // leading
    while ( (len > 0 ) && ( chars[0] == ' ' ) ) {
        char[] newChars = new char[] {}; // initialize empty array
        System.arraycopy(chars, 1, newChars, 0, len - 1);
        chars = newChars;
        len = chars.length;
    }
    // TODO: trailing
    return chars.toString();
}

Answer 1

The simple way to trim leading and trailing whitespace is to call String.trim(). With Java 11 and later, you can also use String.strip() which uses a different interpretation of what "white space" means¹.

If you just want to trim just leading and trailing spaces (rather than all leading and trailing whitespace), there is an Apache commons method called StringUtils.strip(String, String) that can do this; call it with " " as the 2nd argument.

Your attempted code has a number of bugs, and is fundamentally inefficient. If you really want to implement this yourself, then you should:

1. count the leading space characters
2. count the trailing space characters
3. if either count is non-zero, call String.substring(from, end) to create a new string containing the characters you want to keep.

This approach avoids copying any characters².

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^{1 - The different meanings are explained in the respective javadocs. Alternatively, read the answers to Difference between String trim() and strip() methods in Java 11.}

^{2 - Actually, that depends on the implementation of String. For some implementations there will be no copying, for others a single copy is made. But either is an improvement on your approach, which entails a minimum of 2 copies, and more if there are any characters to trim.}

Answer 2

String.trim() is very old, at least to java 1.3. You don't have this?