What is Collectors.toCollection() in Java?
What is the collectors class?
Collectors is a utility class that provides various implementations of reduction operations, such as grouping elements, adding elements to different collections, summarizing elements according to various criteria, and so on. The other functionalities in the Collectors class are usually used as the final operation on streams.
The toCollection() method
toCollection() is a static method of the Collectors class, which is used to collect/accumulate all the elements in a new collection in the encountered order.
The toCollection 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, C extends Collection<T>> Collector<T, ?, C> toCollection(Supplier<C> collectionFactory)
Parameters
Supplier<C> collectionFactory: TheSupplierimplementation provides a new emptyCollectioninto which the elements/results are inserted.
Return value
This method returns a Collector that collects all the elements to a collection.
Code example
import java.util.ArrayList;import java.util.Arrays;import java.util.List;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");System.out.println("Stream before modification - " + stringList);Stream<String> stringStream = stringList.stream();List<String> uppercaseStream = stringStream.map(String::toUpperCase).collect(Collectors.toCollection(ArrayList::new));System.out.println("Stream after modification - " + uppercaseStream);}}
Code explanation
- Lines 1–4: We import the relevant packages.
- Line 10: We define a list of strings called
stringList. - Line 12: We print the
stringList. - Line 14: We create a stream out of the
stringList. - Line 16: We convert the stream elements to uppercase, using the
mapmethod and collect the resulting elements to a newArrayListwith thetoCollectionmethod. - Line 18: We print the new list of uppercase elements.
Note: Refer to the “What is an ArrayList in Java?” shot to learn more about an ArrayList.
