An array of strings can be joined using the static method [String.join()](<https://docs.oracle.com/javase/8/docs/api/java/lang/String.html#join-java.lang.CharSequence-java.lang.CharSequence>...-):

String[] elements = { "foo", "bar", "foobar" };
String singleString = String.join(" + ", elements);

System.out.println(singleString); // Prints "foo + bar + foobar"

Similarly, there’s an overloaded [String.join()](<https://docs.oracle.com/javase/8/docs/api/java/lang/String.html#join-java.lang.CharSequence-java.lang.Iterable->) method for Iterables.

To have a fine-grained control over joining, you may use StringJoiner class:

StringJoiner sj = new StringJoiner(", ", "[", "]"); 
    // The last two arguments are optional, 
    // they define prefix and suffix for the result string

sj.add("foo");
sj.add("bar");
sj.add("foobar");

System.out.println(sj); // Prints "[foo, bar, foobar]"

To join a stream of strings, you may use the joining collector:

Stream<String> stringStream = Stream.of("foo", "bar", "foobar");
String joined = stringStream.collect(Collectors.joining(", "));
System.out.println(joined); // Prints "foo, bar, foobar"

There’s an option to define prefix and suffix here as well:

Stream<String> stringStream = Stream.of("foo", "bar", "foobar");
String joined = stringStream.collect(Collectors.joining(", ", "{", "}"));
System.out.println(joined); // Prints "{foo, bar, foobar}"