CODEWITHSUNDEEP
javaregexarraysstringsplit
James Raitsev
James Raitsev

Reputation: 96531

How to split a String array?

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(",");

Upvotes: 12

Views: 18835

Answers (4)

Jagat
Jagat

Reputation: 1402

If you need to perform this operation repeatedly, I'd suggest using java.util.regex.Pattern and java.util.regex.Matcher instead.

final Pattern pattern = Pattern.compile( regex);
for(String inp: inps) {
    final Matcher matcher = pattern.matcher( inpString);
    return matcher.replaceAll( replacementString); 
}

Compiling a regex is a costly operation and using String's replaceAll repeatedly is not recommended, since each invocation involves compilation of regex followed by replacement.

Upvotes: 0

Paul Tomblin
Paul Tomblin

Reputation: 182880

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.

Upvotes: 6

user85421
user85421

Reputation: 29730

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)

Upvotes: 2

polygenelubricants
polygenelubricants

Reputation: 384006

On regex vs non-regex methods

The String class has the following methods:

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"

Upvotes: 10

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