How to split a String by space

Question

I need to split my String by spaces. For this I tried:

str = \"Hello I\'m your String\";
String[] splited = str.split(\" \");

But it doesn\

Answer 1

While the accepted answer is good, be aware that you will end up with a leading empty string if your input string starts with a white space. For example, with:

String str = " Hello I'm your String";
String[] splitStr = str.split("\\s+");

The result will be:

splitStr[0] == "";
splitStr[1] == "Hello";
splitStr[2] == "I'm";
splitStr[3] == "Your";
splitStr[4] == "String";

So you might want to trim your string before splitting it:

String str = " Hello I'm your String";
String[] splitStr = str.trim().split("\\s+");

[edit]

In addition to the trim caveat, you might want to consider the unicode non-breaking space character (U+00A0). This character prints just like a regular space in string, and often lurks in copy-pasted text from rich text editors or web pages. They are not handled by .trim() which tests for characters to remove using c <= ' '; \s will not catch them either.

Instead, you can use \p{Blank} but you need to enable unicode character support as well which the regular split won't do. For example, this will work: Pattern.compile("\\p{Blank}", UNICODE_CHARACTER_CLASS).split(words) but it won't do the trim part.

The following demonstrates the problem and provides a solution. It is far from optimal to rely on regex for this, but now that Java has 8bit / 16bit byte representation, an efficient solution for this becomes quite long.

public class SplitStringTest
{
    static final Pattern TRIM_UNICODE_PATTERN = Pattern.compile("^\\p{Blank}*(.*)\\p{Blank}$", UNICODE_CHARACTER_CLASS);
    static final Pattern SPLIT_SPACE_UNICODE_PATTERN = Pattern.compile("\\p{Blank}", UNICODE_CHARACTER_CLASS);

    public static String[] trimSplitUnicodeBySpace(String str)
    {
        Matcher trimMatcher = TRIM_UNICODE_PATTERN.matcher(str);
        boolean ignore = trimMatcher.matches(); // always true but must be called since it does the actual matching/grouping
        return SPLIT_SPACE_UNICODE_PATTERN.split(trimMatcher.group(1));
    }

    @Test
    void test()
    {
        String words = " Hello I'm\u00A0your String\u00A0";
        // non-breaking space here --^ and there -----^

        String[] split = words.split(" ");
        String[] trimAndSplit = words.trim().split(" ");
        String[] splitUnicode = SPLIT_SPACE_UNICODE_PATTERN.split(words);
        String[] trimAndSplitUnicode = trimSplitUnicodeBySpace(words);

        System.out.println("words: [" + words + "]");
        System.out.println("split: [" + Arrays.stream(split).collect(Collectors.joining("][")) + "]");
        System.out.println("trimAndSplit: [" + Arrays.stream(trimAndSplit).collect(Collectors.joining("][")) + "]");
        System.out.println("splitUnicode: [" + Arrays.stream(splitUnicode).collect(Collectors.joining("][")) + "]");
        System.out.println("trimAndSplitUnicode: [" + Arrays.stream(trimAndSplitUnicode).collect(Collectors.joining("][")) + "]");
    }
}

Results in:

words: [ Hello I'm your String ]
split: [][Hello][I'm your][String ]
trimAndSplit: [Hello][I'm your][String ]
splitUnicode: [][Hello][I'm][your][String]
trimAndSplitUnicode: [Hello][I'm][your][String]