Java 8 StringJoiner demo

24 01 2016

Finally Java has convenient and intuitive API for joining strings with delimiters! Since Java 8 there is StringJoiner class. It is an API that you may know from Guava Joiner classes (see my post: https://looksok.wordpress.com/2015/10/17/guava-joiner-join-all-strings-in-an-array-or-map/). Here is a short StringJoiner demo.

Basic String joins

The most basic usage is to create StringJoiner instance with delimiter as a constructor param and add() strings:

StringJoiner joiner = new StringJoiner(",");
joiner.add("apple");
joiner.add("banana");
joiner.add("orange");

System.out.println("Joiner result is: " + joiner.toString());

The result is:

Joiner result is: apple,banana,orange

If you prefer, you can chain add() calls:

StringJoiner joiner = new StringJoiner(",")
    .add("apple")
    .add("banana")
    .add("orange");

Join Collection of Strings

If you have Collection of Strings, the new static String.join() method can join them:

List<String> list = Arrays.asList("apple", "banana", "orange");
String joined = String.join(", ", list);

System.out.println("Join Array result is: " + joined);

With the result of:

Join Array result is: apple, banana, orange

Join inline

You can prepare joined String in one line with String.join() overloaded with varargs, like that:

String.join(", ", "apple", "banana", "orange");

Joining Collector in Stream API

When using streams you have joining Collector at your disposal:

List<String> list = Arrays.asList("apple", "banana", "orange");
String joined = list.stream()
        .collect(Collectors.joining(", "));

System.out.println("Joined with collector: " + joined);

This will result with:

Joined with collector: apple, banana, orange

Source Code

As always, I share with you the source code for this demo on my github: https://github.com/yacekmm/looksok/tree/StringJoinerDemo/Java/JavaDemo

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