A use case that comes across frequently, is creating a String from a stream, where the stream-items are separated by a certain character. The Collectors.joining() method can be used for this, like in the following example:
Stream<String> fruitStream = Stream.of("apple", "banana", "pear", "kiwi", "orange");
String result = fruitStream.filter(s -> s.contains("a"))
.map(String::toUpperCase)
.sorted()
.collect(Collectors.joining(", "));
System.out.println(result);Output:
APPLE, BANANA, ORANGE, PEAR
The Collectors.joining() method can also cater for pre- and postfixes:
String result = fruitStream.filter(s -> s.contains("e"))
.map(String::toUpperCase)
.sorted()
.collect(Collectors.joining(", ", "Fruits: ", "."));
System.out.println(result);Output:
Fruits: APPLE, ORANGE, PEAR.