Java 25 (LTS) reference · Stream API

Java Collectors.joining() Method

Join a stream of strings into one string, with an optional separator, prefix and suffix.

Java 25 (LTS) Since Java 8

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Syntax

stream.collect(Collectors.joining(delimiter, prefix, suffix))

Parameters

Parameter	Description
`delimiter, prefix, suffix` optional CharSequence	Text between, before and after the elements.

Return value

A String.

Examples

Join with separators

import java.util.*;
import java.util.stream.*;

public class Main {
    public static void main(String[] args) {
        System.out.println(Stream.of("Java", "Kotlin", "Scala").collect(Collectors.joining(", ")));
        System.out.println(Stream.of("a", "b").collect(Collectors.joining("|", "[", "]")));
    }
}

Output

Java, Kotlin, Scala
[a|b]

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Summarise objects

import java.util.*;
import java.util.stream.*;

public class Main {
    public static void main(String[] args) {
        record Item(String name, int qty) {}
        List<Item> cart = List.of(new Item("mug", 2), new Item("tea", 1));
        System.out.println(cart.stream().map(i -> i.qty() + "x " + i.name()).collect(Collectors.joining("; ")));
    }
}