Join strings with different separators in Java

Question

I have a list of strings, e.g. days of the week. And I'd like to join them on comma, with "and" before the last element. E.g: "I'm available on Tue, Wed, Thu and Fri".

Something elegant like

Joiner.on(", ").join(days)

Does not work. Is there an elegant way to do it with Guava or similar library?

Thanks

Answer 1

Java 6/7 compatible solution using Guava:

static String join(List<String> strings, String separator, String lastSeparator)
{
    checkNotNull(strings);
    switch (strings.size()) {
        case 0:
            return "";
        case 1:
            return strings.get(0);
        default:
            return Joiner.on(separator).join(strings.subList(0, strings.size() - 1))
                    + lastSeparator + strings.get(strings.size() - 1);
    }
}

or if you want to accept Iterable (and / or use more Guava stuff):

static String join(Iterable<String> strings, String separator, String lastSeparator)
{
    checkNotNull(strings);
    int size = Iterables.size(strings);
    switch (size) {
        case 0:
            return "";
        case 1:
            return strings.iterator().next();
        default:
            return Joiner.on(separator).join(Iterables.limit(strings, size - 1))
                    + lastSeparator + Iterables.getLast(strings);
    }
}

It handles all edge cases except null elements in strings - if you want to handle them and not throw NPE, add .useForNull(stringForNull) to your joiner.

Answer 2

Courtesy to Java having replaceFirst but no replaceLast, and assuming "_,_" will not appear in any of the elements/parts, I hacked the following function:

public static String join(Iterable<?> parts) {
    String reverse = new StringBuilder(Joiner.on("_,_").join(parts)).reverse().toString();
    reverse = reverse.replaceFirst("_,_", " dna ").replaceAll("_,_", " ,");
    return new StringBuilder(reverse).reverse().toString();
}

And then:

System.out.println(join(Arrays.asList("One", "Two", "Three", "Four")));

Gives: One, Two, Three and Four

Answer 3

Considering you're "not Java 8 friendly at this moment" (you probably mean lambdas and streams), how about using StringJoiner:

public static String join(List<String> parts, String delimiter, String lastDelimiter) {
    StringJoiner joiner = new StringJoiner(delimiter, "", lastDelimiter);

    for (int i = 0; i < parts.size() - 1; i++) {
        joiner.add(parts.get(i));
    }

    return joiner.toString() + parts.get(parts.size() - 1);
}

However, doing the same with streams:

public static String join(List<String> parts, String delimiter, String lastDelimiter) {
    return parts.stream()
            .limit(parts.size() - 1)
            .collect(Collectors.joining(delimiter, "", lastDelimiter))
            .concat(parts.get(parts.size() - 1));
}

EDIT: Just found String#join(CharSequence, Iterable<? extends CharSequence>):

public static String join(List<String> parts, String delimiter, String lastDelimiter) {
    return String.join(delimiter, parts.subList(0, parts.size() - 1)) 
            + lastDelimiter + parts.get(parts.size() - 1);
}

In order to handle corner cases I'd go for Xaerxess switch solution.

Answer 4

There is no straightforward solution, but you may consider mine:

final String COMMA = ", ", AND = " and ";
List<String> list = Arrays.asList("Tue", "Wed", "Thu", "Fri");
int last = list.size() - 1;

Joiner.on(AND).join(
    list.stream().limit(last).collect(joining(COMMA)),
    list.get(last)); // Tue, Wed, Thu and Fri

The another shorter way is:

list.stream().limit(last).collect(joining(COMMA, "", AND))
    .concat(list.get(last));

These methods perfectly work for 2+ days.

Edge cases (list == null || list.isEmpty() and list.size() < 2) may be handled by the if statements.