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Collectors toSet() in Java with Examples

Last Updated : 06 Dec, 2018
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Collectors toSet() returns a Collector that accumulates the input elements into a new Set. There are no guarantees on the type, mutability, serializability, or thread-safety of the Set returned. This is an unordered Collector i.e, the collection operation does not commit to preserving the encounter order of input elements. Syntax: 
public static <T> Collector<T, ?, Set<T>> toSet()
where:
  • T: The type of the input elements.
  • Interface Collector<T, A, R>: A mutable reduction operation that accumulates input elements into a mutable result container, optionally transforming the accumulated result into a final representation after all input elements have been processed. Reduction operations can be performed either sequentially or in parallel.
    • T: The type of input elements to the reduction operation.
    • A: The mutable accumulation type of the reduction operation.
    • R: The result type of the reduction operation.
  • Set: A collection that contains no duplicate elements. More formally, sets contain no pair of elements e1 and e2 such that e1.equals(e2), and at most one null element.
Return Value: A Collector which collects all the input elements into a Set. Below are the examples to illustrate toSet() method: Example 1: Java 
// Java code to show the implementation of
// Collectors toSet() function

import java.util.Set;
import java.util.stream.Collectors;
import java.util.stream.Stream;

class GFG {

    // Driver code
    public static void main(String[] args)
    {
        // creating a Stream of strings
        Stream<String> s = Stream.of("Geeks",
                                     "for",
                                     "GeeksforGeeks",
                                     "Geeks Classes");

        // using Collectors toSet() function
        Set<String> mySet = s.collect(Collectors.toSet());

        // printing the elements
        System.out.println(mySet);
    }
}
Output: 
[Geeks Classes, GeeksforGeeks, Geeks, for]
Example 2: Java 
// Java code to show the implementation of
// Collectors toSet() function

import java.util.Set;
import java.util.stream.Collectors;
import java.util.stream.Stream;

class GFG {

    // Driver code
    public static void main(String[] args)
    {

        // creating a Stream of strings
        Stream<String> s = Stream.of("1", "2", "3", "4");

        // using Collectors toSet() function
        Set<String> mySet = s.collect(Collectors.toSet());

        // printing the elements
        System.out.println(mySet);
    }
}
Output: 
[1, 2, 3, 4]

S

Sahil_Bansall
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