What is the Collectors.toSet() method in Java?

Collectors class

Collectors is a utility class, which provides various implementations of reduction operations, such as grouping elements, collecting elements to different collections, summarizing elements according to various criteria, and so on. The different functionalities in the Collectors class are usually used as the final operation on streams.

`toSet()` method

toSet() is a static method of the Collectors class, which is used to collect/accumulate all the elements to a new Set. The type, mutability, serializability, and thread-safety of the Set that is returned are not guaranteed.

The toSet method is defined in the Collectors class. The Collectors class is defined in the java.util.stream package. To import the Collectors class, we check the following import statement:

import java.util.stream.Collectors;

Syntax

public static <T> Collector<T, ?, Set<T>> toSet()

Parameters

This method has no parameters.

Return value

This method returns a Collector that collects all the input elements to a Set in the encountered order.

import java.util.Arrays;
import java.util.List;
import java.util.Set;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class Main {
    public static void main(String[] args)
    {
        List<String> stringList = Arrays.asList("educative", "io", "edpresso", "educative", "io", "edpresso");
        System.out.println("Stream before modification - " + stringList);
        Stream<String> stringStream = stringList.stream();
        Set<String> uppercaseSet = stringStream.map(String::toUpperCase).collect(Collectors.toSet());
        System.out.println("Resulting set after modification - " + uppercaseSet);
    }
}