A quick and easy way to join array elements with a

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• Java: function for arrays like PHP's join()? 22 answers

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I'm looking for a quick and easy way to do exactly the opposite of split so that it will cause ["a","b","c"] to become "a,b,c"

Iterating through an array requires either adding a condition (if this is not the last element, add the seperator) or using substring to remove the last separator.

I'm sure there is a certified, efficient way to do it (Apache Commons?)

How do you prefer doing it in your projects?

Answer 1

A fast and simple solution without any 3rd party includes.

public static String strJoin(String[] aArr, String sSep) {
    StringBuilder sbStr = new StringBuilder();
    for (int i = 0, il = aArr.length; i < il; i++) {
        if (i > 0)
            sbStr.append(sSep);
        sbStr.append(aArr[i]);
    }
    return sbStr.toString();
}

Answer 2

If you're on Android you can TextUtils.join(delimiter, tokens)

Answer 3

You can use replace and replaceAll with regular expressions.

String[] strings = {"a", "b", "c"};

String result = Arrays.asList(strings).toString().replaceAll("(^\\[|\\]$)", "").replace(", ", ",");

Because Arrays.asList().toString() produces: "[a, b, c]", we do a replaceAll to remove the first and last brackets and then (optionally) you can change the ", " sequence for "," (your new separator).

A stripped version (fewer chars):

String[] strings = {"a", "b", "c"};

String result = ("" + Arrays.asList(strings)).replaceAll("(^.|.$)", "").replace(", ", "," );

Regular expressions are very powerful, specially String methods "replaceFirst" and "replaceAll". Give them a try.

Answer 4

This small function always comes in handy.

public static String join(String[] strings, int startIndex, String separator) {
    StringBuffer sb = new StringBuffer();
    for (int i=startIndex; i < strings.length; i++) {
        if (i != startIndex) sb.append(separator);
        sb.append(strings[i]);
    }
    return sb.toString();
}

Answer 5

Apache Commons Lang does indeed have a StringUtils.join method which will connect String arrays together with a specified separator.

For example:

String[] s = new String[] {"a", "b", "c"};
String joined = StringUtils.join(s, ",");  // "a,b,c"

However, I suspect that, as you mention, there must be some kind of conditional or substring processing in the actual implementation of the above mentioned method.

If I were to perform the String joining and didn't have any other reasons to use Commons Lang, I would probably roll my own to reduce the number of dependencies to external libraries.

Answer 6

"I'm sure there is a certified, efficient way to do it (Apache Commons?)"

yes, apparenty it's

StringUtils.join(array, separator)

http://www.java2s.com/Code/JavaAPI/org.apache.commons.lang/StringUtilsjoinObjectarrayStringseparator.htm