The Java Streams API provides a powerful and concise way to process collections of data. In addition to its functionality for data processing, it’s also possible to create immutable collections using the Streams API. In this article, we will explore how to create immutable collections using the Java Streams API.

Immutable List

To create an immutable list using the Java Streams API, you can use the collect method with the Collectors.toList() collector. The collect method allows you to accumulate the elements of a stream into a collection. Here’s an example:

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

public class ImmutableCollectionExample {
    public static void main(String[] args) {
        List<Integer> numbers = Stream.of(1, 2, 3, 4, 5)
                .collect(Collectors.toList());

        // Attempting to modify the list will result in an UnsupportedOperationException
        numbers.add(6);  // Throws UnsupportedOperationException
    }
}

In the above example, we create an immutable list numbers by collecting the elements of a stream into a list using the Collectors.toList() collector. Since the list is immutable, any attempt to modify it, such as adding an element, will result in an UnsupportedOperationException.

Immutable Set

Similarly, you can create an immutable set using the Java Streams API by using the collect method with the Collectors.toSet() collector. Here’s an example:

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

public class ImmutableCollectionExample {
    public static void main(String[] args) {
        Set<String> fruits = Stream.of("apple", "banana", "orange")
                .collect(Collectors.toSet());

        // Attempting to modify the set will result in an UnsupportedOperationException
        fruits.add("mango");  // Throws UnsupportedOperationException
    }
}

In the above example, we use the Collectors.toSet() collector to collect the elements of a stream into an immutable set fruits. As with the immutable list example, any attempt to modify the set will result in an UnsupportedOperationException.

Conclusion

The Java Streams API provides a convenient way to create immutable collections. By using the collect method with appropriate collectors such as Collectors.toList() and Collectors.toSet(), you can easily create immutable lists and sets. Immutable collections offer advantages in terms of thread-safety, security, and easy debugging.

#immutablecollections #javastreams