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(",");

Answer 1

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"