How to split a String array?

Question

Intention is to take a current line (String that contains commas), replace white space with "" (Trim space) and finally store split String elements into the array.

Why does not this work?

String[] textLine = currentInputLine.replace("\\s", "").split(",");

Solution 1

I think you want replaceAll rather than replace.

And replaceAll("\\s","") will remove all spaces, not just the redundant ones. If that's not what you want, you should try replaceAll("\\s+","\\s") or something like that.

Solution 2

On regex vs non-regex methods

The String class has the following methods:

• Non-regex methods:
  • String replace(char oldChar, char newChar)
  • String replace(CharSequence target, CharSequence replacement)
  • boolean startsWith(String prefix)
  • boolean endsWith(String suffix)
  • boolean contains(CharSequence s)
• Regex methods:
  • String replaceAll(String regex, String replacement)
  • String replaceFirst(String regex, String replacement)
  • String[] split(String regex)
  • boolean matches(String regex)

So here we see the immediate cause of your problem: you're using a regex pattern in a non-regex method. Instead of replace, you want to use replaceAll.

Other common pitfalls include:

• split(".") (when a literal period is meant)
• matches("pattern") is a whole-string match!
  • There's no contains("pattern"); use matches(".*pattern.*") instead

---

On Guava's Splitter

Depending on your need, String.replaceAll and split combo may do the job adequately. A more specialized tool for this purpose, however, is Splitter from Guava.

Here's an example to show the difference:

public static void main(String[] args) {
    String text = "  one, two, , five (three sir!) ";

    dump(text.replaceAll("\\s", "").split(","));
    // prints "[one] [two] [] [five(threesir!)] "

    dump(Splitter.on(",").trimResults().omitEmptyStrings().split(text));
    // prints "[one] [two] [five (three sir!)] "
}

static void dump(String... ss) {
    dump(Arrays.asList(ss));
}
static void dump(Iterable<String> ss) {
    for (String s : ss) {
        System.out.printf("[%s] ", s);
    }
    System.out.println();       
}

Note that String.split can not omit empty strings in the beginning/middle of the returned array. It can omit trailing empty strings only. Also note that replaceAll may "trim" spaces excessively. You can make the regex more complicated, so that it only trims around the delimiter, but the Splitter solution is definitely more readable and simpler to use.

Guava also has (among many other wonderful things) a very convenient Joiner.

System.out.println(
    Joiner.on("... ").skipNulls().join("Oh", "My", null, "God")
);
// prints "Oh... My... God"

Solution 3

What you wrote does not match the code:

Intention is to take a current line which contains commas, store trimmed values of all space and store the line into the array.

It seams, by the code, that you want all spaces removed and split the resulting string at the commas (not described). That can be done as Paul Tomblin suggested.

String[] currentLineArray = currentInputLine.replaceAll("\\s", "").split(",");

If you want to split at the commas and remove leading and trailing spaces (trim) from the resulting parts, use:

String[] currentLineArray = currentInputLine.trim().split("\\s*,\\s*");

(trim() is needed to remove leading spaces of first part and trailing space from last part)

Comments

[user85421]

"\s" is not a valid Java String. It should be "\\s" (same for "\\s+")

[Paul Tomblin]

@Carlos - interestingly, that's what I wrote, but because I didn't put it in code marks, it showed it as \s instead of \\s.

[tchrist]

First, you can’t use a regexp in the replacement, only in the search part. Second, this doesn’t remove all whitespace, because it misses common non-ASCII whitespace code points like U+00A0 NO-BREAK SPACE due to a Java bug not fixed till Java 7, and even then you have to embed a "(?U)" into your pattern to get \s to match Unicode whitespace. If you’re used to languages like Perl whose regexes already pick up Unicode by default, it is easy to miss that they do not do so in Java.