Collectors is a utility class that provides various implementations of reduction operations, such as grouping elements, adding them to different collections, summarizing them according to various criteria, etc. The different functionalities in the Collectors class are usually used as the final operation on streams.
toUnmodifiableSet() is a static method of the Collectors class that collects or accumulates all the elements to a new unmodifiable set. This method returns a Collector that disallows null values, and raises a NullPointerException if supplied with null values. If any duplicate elements are present, this method retains an arbitrary instance of the duplicates. This method was introduced in Java 10.
The toUnmodifiableSet method is defined in the Collectors class which is defined in the java.util.stream package. To import the Collectors class, we use the following import statement.
import java.util.stream.Collectors;
public static <T> Collector<T, ?, Set<T>> toUnmodifiableSet()
The method has no parameters.
This method returns a collector that collects all the input elements into an unmodifiable set in the encounter 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.toUnmodifiableSet());System.out.println("Resulting set after modification - " + uppercaseSet);uppercaseSet.add("test");}}
stringList.stringList.stringList.map method. We then collect the resulting elements to a new unmodifiable set, using the toUnmodifiableSet method.