Collectors collectingAndThen() method in Java 8

The collectingAndThen() method in Java Collectors class acclimates a Collector to perform an additional finishing transformation. It returns collector which performs the action of the downstream collector, followed by an additional ending step.

The syntax is as follows.

static <T,A,R,RR> Collector<T,A,RR> collectingAndThen(Collector<T,A,R> downstream, Function<R,RR> finisher)

Here, the parameter,

• T − Type of the input elements

• A − Intermediate accumulation type of the downstream collector

• R − The result type of the downstream collector

• RR − The result type of the resulting collector

• downstream − Collector

• finisher − A function to be applied to the final result of the downstream collector

To work with Collectors class in Java, import the following package.

import java.util.stream.Collectors;

The following is an example to implement collectingAndThen() method in Java.

Example

 Live Demo

import java.util.List; import java.util.Collections; import java.util.stream.Collectors; import java.util.stream.Stream; public class Demo {    public static void main(String[] args) {       List<String> list       = Stream.of("Demo1", "Demo2").collect(Collectors.collectingAndThen(       Collectors.toList(),       Collections::<String> unmodifiableList));       System.out.println(list);    } }

Output

[Demo1, Demo2]