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String Joiner is being used for joining the strings with the use of delimiter, prefix and postfix.

String Joiner is very useful when you need to join strings in a parallel stream.

package com.praveen.others;

import java.util.Arrays;
import java.util.List;
import java.util.StringJoiner;
import java.util.stream.Collectors;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.ToString;
import lombok.experimental.SuperBuilder;

@AllArgsConstructor
@Data
@SuperBuilder
@ToString
class Game {
	private final String name;
	private final int ranking;

}

public class StringJoinExample {

	public static void main(String args[]) {
		// Join String by a delimiter
		StringJoiner sj = new StringJoiner(",");
		sj.add("aaa");
		sj.add("bbb");
		sj.add("ccc");
		System.out.println(sj);
		// Join String by a delimiter and starting with a supplied prefix and ending
		// with a supplied suffix.
		StringJoiner sj1 = new StringJoiner("/", "[", "]");
		sj1.add("2016");
		sj1.add("02");
		sj1.add("26");
		System.out.println(sj1);
		// StringJoiner is used internally by static String.join().
		// Join String by a delimiter.
		System.out.println(String.join("-", "2015", "10", "31"));
		// Join a List by a delimiter.

		List<String> list = Arrays.asList("java", "python", "nodejs", "ruby");
		// java: python: nodejs: ruby
		System.out.println(String.join(": ", list));

		// Collectors.joining
		// Join List<String> example.

		// java | python | nodejs | ruby
		System.out.println(list.stream().map(x -> x).collect(Collectors.joining(" | ")));

		// Join List<Object> example

		List<Game> listGame = Arrays.asList(new Game("Dragon Blaze", 5), new Game("Angry Bird", 5),
				new Game("Candy Crush", 5));

		// {Dragon Blaze, Angry Bird, Candy Crush}
		System.out.println(listGame.stream().map(Game::getName).collect(Collectors.joining(", ", "{", "}")));

	}

}