Java Stream Operations Simplified - Part 2

In this post, we will look at some of the terminal stream operations. A terminal operation is applied to the end of intermediate operations. They help to return a result from a stream.

Terminal Operations

Taking our previous example of list of pets and adding more pets.

List<Pet> myPets =
        List.of(
                new Pet("Molly", Type.CAT, 2),
                new Pet("Jimmy", Type.DOG, 3),
                new Pet("Rocky", Type.DOG, 3),
                new Pet("Chirpie", Type.BIRD, 5),
                new Pet("Rabbu", Type.RABBIT, 1),
        );

• count()

This operation will return the number of elements in the stream.

myPets
     .stream()
     .filter(p -> p.type.equals(Type.DOG))
     .count(); 
// 2

• forEach()

This method is used to iterate through the elements of the stream. It does not return any value.

myPets
     .stream()
     .forEach(p -> System.out.println(p.getName()));
// Molly
// Jimmy
// Rocky
// Chirpie
// Rabbu

• collect()

This method is used to iterate through the elements of the stream and then collect them into a collection or some kind of object.

List<Pet> seniorPets = myPets
     .stream()
     .filter(p -> p.getAge > 2)
     .collect(Collectors.toList());

// This will create a new collection where the ages of pets are greater than 2

• max()

This method is used to return the maximum element in the stream according to the specified comparator.

Optional<Pet> optionalPet = myPets
     .stream()
     .max((p1, p2) -> p1.getAge() - p2.getAge());

// max() returns an optional

if (optionalPet.isPresent()) {
    System.out.print(optionalPet.get().getName());
}

// This will return a pet which is the oldest

• min()

This operation is the opposite of max(). This method is used to return the minimum element in the stream according to the specified comparator.

Optional<Pet> optionalPet = myPets
     .stream()
     .min((p1, p2) -> p1.getAge() - p2.getAge());

// min() returns an optional

if (optionalPet.isPresent()) {
    System.out.print(optionalPet.get().getName());
}
// This will return the youngest pet
// Rabbu

• reduce()

This operation is used to reduce all elements in the stream to a single element.

Optional<String> names = myPets
     .stream()
     .reduce((p1, p2) -> p1.getName()+" , "+p2.getName());


if (names.isPresent()) {
    System.out.print(optionalPet.get());
}
// Molly, Jimmy, Rocky, Chirpie, Rabbu

Conclusion

In this post, we looked briefly upon some terminal stream operations. For detailed information, please refer to the official Java Docs.