Fastest way to put contents of Set<String> to a single String with words separated by a whitespace?

Question

I have a few Set<String>s and want to transform each of these into a single String where each element of the original Set is separated by a whitespace " ". A naive first approach is doing it like this

Set<String> set_1;
Set<String> set_2;

StringBuilder builder = new StringBuilder();
for (String str : set_1) {
  builder.append(str).append(" ");
}

this.string_1 = builder.toString();

builder = new StringBuilder();
for (String str : set_2) {
  builder.append(str).append(" ");
}

this.string_2 = builder.toString();

Can anyone think of a faster, prettier or more efficient way to do this?

Answer 1

I'm confused about the code replication, why not factor it into a function that takes one set and returns one string?

Other than that, I'm not sure that there is much that you can do, except maybe giving the stringbuilder a hint about the expected capacity (if you can calculate it based on set size and reasonable expectation of string length).

There are library functions for this as well, but I doubt they're significantly more efficient.

Answer 2

With commons/lang you can do this using StringUtils.join:

String str_1 = StringUtils.join(set_1, " ");

You can't really beat that for brevity

Answer 3

As a counterpoint to Seanizer's commons-lang answer, if you're using Google's Guava Libraries (which I'd consider the 'successor' to commons-lang, in many ways), you'd use Joiner:

Joiner.on(" ").join(set_1);

with the advantage of a few helper methods to do things like:

Joiner.on(" ").skipNulls().join(set_1);
// If 2nd item was null, would produce "1, 3"

or

Joiner.on(" ").useForNull("<unknown>").join(set_1);
// If 2nd item was null, would produce "1, <unknown>, 3"

It also has support for appending direct to StringBuilders and Writers, and other such niceties.