Last Updated on August 3, 2023 by Mayank Dham
Java 8 introduced a powerful feature called Streams, revolutionizing the way we process collections and perform data manipulation in Java. Streams provide a functional and declarative approach to working with data, allowing developers to write concise and expressive code. In this article, we will explore the key concepts and functionalities of Java 8 Streams, uncovering how they simplify data processing and enable efficient streamlining of operations.
Understanding Java 8 Stream
Java 8 Streams are a sequence of elements that can be processed in a declarative and functional manner. Unlike traditional collections, Streams allow for efficient parallel processing, lazy evaluation, and streamlined operations. Streams provide a higher-level abstraction, enabling developers to focus on the "what" instead of the "how" of data processing.
Features of Java 8 Streams
Java 8 Streams introduced several powerful features that revolutionized data processing in Java. Here are some key features of Java 8 Streams:
1. Declarative and Functional Programming:
Java 8 Streams allow developers to write code in a declarative and functional style. With streams, the focus is on specifying the desired operations rather than the detailed implementation. This leads to more expressive and readable code that is easier to maintain and understand.
2. Sequential and Parallel Processing:
Streams provide seamless support for both sequential and parallel processing. Sequential streams process elements one by one in a single thread, while parallel streams leverage multiple threads to divide the workload and process elements concurrently. This enables efficient utilization of multi-core processors and can significantly improve performance for computationally intensive tasks.
3. Lazy Evaluation:
Streams exhibit lazy evaluation, which means that intermediate operations are only executed when a terminal operation is invoked. This allows for efficient processing by avoiding unnecessary computations. Lazy evaluation provides optimization opportunities, especially when working with large or infinite data sets.
4. Stream Pipelines:
Stream operations can be combined into pipelines, where the result of one operation becomes the input for the next operation. This allows for the creation of expressive and concise code by chaining multiple operations together. Stream pipelines make it easy to perform complex data transformations and manipulations in a readable manner.
Java 8 Streams have transformed the way developers work with collections and perform data processing in Java. With their declarative style, support for parallel processing, and efficient lazy evaluation, Streams have become an essential tool for writing clean, efficient, and expressive code in Java.
How does a Stream function internally?
In streams,
- To filter out objects, we have a function called filter().
- To impose a condition, we have predicate logic, which is nothing more than a functional interface. A random expression can be used to replace the function interface in this case. As a result, we can impose the condition check-in on our predicate directly.
- To collect elements, we will use Collectors.toList() to gather all of the necessary elements.
- Finally, we will store these elements in a List and output the results to the console.
Various Core Operations that are done on Stream
Java 8 Streams provide a wide range of core operations that can be applied to process data in a declarative and functional manner. Here are the core operations commonly used with Java 8 Streams:
1. Filter:
The filter() operation allows you to select elements from a stream based on a given predicate. It takes a lambda expression that evaluates each element and returns a boolean value to determine if the element should be included in the resulting stream.
2. Map:
The map() operation transforms each element in a stream by applying a mapping function to it. It takes a lambda expression that specifies the transformation logic and produces a new stream containing the transformed elements.
3. FlatMap:
The flatMap() operation is used to flatten nested streams. It maps each element of a stream to a new stream and then combines all the resulting streams into a single stream.
4. Sorted:
The sorted() operation sorts the elements of a stream in a specified order. It can take a comparator to define the sorting order, or it can rely on the natural ordering of the elements if they implement the Comparable interface.
5. forEach:
The forEach() operation performs an action on each element of a stream. It takes a lambda expression specifying the action to be performed on each element.
6. Reduce:
The reduce() operation combines the elements of a stream into a single value. It takes an identity value and a binary operator, which are applied to each element successively to produce the final result.
7. Collect:
The collect() operation accumulates the elements of a stream into a collection or a single value. It takes a Collector to define the rules for accumulation, such as grouping, partitioning, or joining elements.
8. Count:
The count() operation returns the number of elements in a stream as a long value.
9. AnyMatch, AllMatch, NoneMatch:
These operations are used to check if elements of a stream satisfy a given condition. anyMatch() returns true if at least one element matches the condition, allMatch() returns true if all elements match the condition, and noneMatch() returns true if no elements match the condition.
These core operations can be combined in various ways to form powerful stream pipelines, enabling efficient and expressive data processing in Java.
Java 8 Stream Interface Methods
Here is a complete list of methods that are applicable to Java 8 stream
| Methods | Description |
|---|---|
| boolean allMatch(Predicate<? super T> predicate) | It returns all elements of this stream that match the provided predicate. If the stream is empty, then true is returned and the predicate is not evaluated. |
| boolean anyMatch(Predicate<? super T> predicate) | It returns any element of this stream that matches the provided predicate. If the stream is empty, then false is returned and the predicate is not evaluated. |
| static |
It returns a builder for a Stream. |
| <R,A> R collect(Collector<? super T,A,R> collector) | It performs a mutable reduction operation on the elements of this stream using a Collector. A Collector encapsulates the functions used as arguments to collect (Supplier, BiConsumer, BiConsumer), allowing for reuse of collection strategies and composition of collect operations such as multiple-level grouping or partitioning. |
| It performs a mutable reduction operation on the elements of this stream. A mutable reduction is one in which the reduced value is a mutable result container, such as an ArrayList, and elements are incorporated by updating the state of the result rather than by replacing the result. | |
| static |
It creates a lazily concatenated stream whose elements are all the elements of the first stream, followed by all the elements of the second stream. The resulting stream is ordered if both of the input streams are ordered, and parallel if either of the input streams is parallel. When the resulting stream is closed, the close handlers for both input streams are invoked. |
| long count() | It returns the count of elements in this stream. This is a special case of a reduction. |
| Stream |
It returns a stream consisting of the distinct elements (according to Object.equals(Object)) of this stream. |
| static |
It returns an empty sequential Stream. |
| Stream |
It returns a stream consisting of the elements of this stream that match the given predicate. |
| Optional |
It returns an Optional describing some element of the stream, or an empty Optional if the stream is empty. |
| Optional |
It returns an Optional describing the first element of this stream, or an empty Optional if the stream is empty. If the stream has no encounter order, then any element may be returned. |
| It returns a stream consisting of the results of replacing each element of this stream with the contents of a mapped stream produced by applying the provided mapping function to each element. Each mapped stream is closed after its contents have been placed into this stream. (If a mapped stream is null, an empty stream is used, instead.) | |
| DoubleStream flatMapToDouble(Function<? super T,? extends DoubleStream> mapper) | It returns a DoubleStream consisting of the results of replacing each element of this stream with the contents of a mapped stream produced by applying the provided mapping function to each element. Each mapped stream is closed after its contents have been placed into this stream. (If a mapped stream is null an empty stream is used, instead.) |
| IntStream flatMapToInt(Function<? super T,? extends IntStream> mapper) | It returns an IntStream consisting of the results of replacing each element of this stream with the contents of a mapped stream produced by applying the provided mapping function to each element. Each mapped stream is closed after its contents have been placed into this stream. (If a mapped stream is null, an empty stream is used, instead.) |
| LongStream flatMapToLong(Function<? super T,? extends LongStream> mapper) | It returns a LongStream consisting of the results of replacing each element of this stream with the contents of a mapped stream produced by applying the provided mapping function to each element. Each mapped stream is closed after its contents have been placed into this stream. (If a mapped stream is null, an empty stream is used, instead.) |
| void forEach(Consumer<? super T> action) | It performs an action for each element of this stream. |
| void forEachOrdered(Consumer<? super T> action) | It performs an action for each element of this stream, in the encounter order of the stream, if the stream has a defined encounter order. |
| static |
It returns an infinite, sequential, unordered stream where each element is generated by the provided Supplier. This is suitable for generating constant streams, streams of random elements, etc. |
| static |
It returns an infinite sequentially ordered Stream produced by iterative application of a function f to an initial element seed, producing a Stream consisting of seed, f(seed), f(f(seed)), etc. |
| Stream |
It returns a stream consisting of the elements of this stream, truncated to be no longer than maxSize in length. |
| It returns a stream consisting of the results of applying the given function to the elements of this stream. | |
| DoubleStream mapToDouble(ToDoubleFunction<? super T> mapper) | It returns a DoubleStream consisting of the results of applying the given function to the elements of this stream. |
| IntStream mapToInt(ToIntFunction<? super T> mapper) | It returns an IntStream consisting of the results of applying the given function to the elements of this stream. |
| LongStream mapToLong(ToLongFunction<? super T> mapper) | It returns a LongStream consisting of the results of applying the given function to the elements of this stream. |
| Optional |
It returns the maximum element of this stream according to the provided Comparator. This is a special case of reduction. |
| Optional |
It returns the minimum element of this stream according to the provided Comparator. This is a special case of reduction. |
| boolean noneMatch(Predicate<? super T> predicate) | It returns elements of this stream that match the provided predicate. If the stream is empty, then true is returned and the predicate is not evaluated. |
| @SafeVarargs static |
It returns a sequentially ordered stream whose elements are the specified values. |
| static |
It returns a sequential Stream containing a single element. |
| Stream |
It returns a stream consisting of the elements of this stream, additionally performing the provided action on each element as elements are consumed from the resulting stream. |
| Optional |
It performs a reduction on the elements of this stream, using an associative accumulation function, and returns an Optional describing the reduced value, if any. |
| T reduce(T identity, BinaryOperator |
It performs a reduction on the elements of this stream, using the provided identity value and an associative accumulation function, and returns the reduced value. |
| U reduce(U identity, BiFunction<U,? super T,U> accumulator, BinaryOperator combiner) | It performs a reduction on the elements of this stream, using the provided identity, accumulation, and combining functions. |
| Stream |
It returns a stream consisting of the remaining elements of this stream after discarding the first n elements of the stream. If this stream contains fewer than n elements, then an empty stream will be returned. |
| Stream |
It returns a stream consisting of the elements of this stream, sorted according to their natural order. If the elements of this stream are not Comparable, a java.lang.ClassCastException may be thrown when the terminal operation is executed. |
| Stream |
It returns a stream consisting of the elements of this stream, sorted according to the provided Comparator. |
| Object[] toArray() | It returns an array containing the elements of this stream. |
| A[] toArray(IntFunction<A[]> generator) | It returns an array containing the elements of this stream, using the provided generator function to allocate the returned array, as well as any additional arrays that might be required for a partitioned execution or for resizing. |
Code Examples of Java 8 Stream
We will be discussing various implementations of streams that are most commonly used in Java 8 stream.
1. Filtering Collection without Using Stream:
In this code example, a collection of products is filtered based on a condition using a traditional for-each loop. The filtered elements are added to a separate list.
List productsList = new ArrayList();
// Adding Products...
List filteredProducts = new ArrayList();
for (Product product : productsList) {
if (product.getPrice() < 30000) {
filteredProducts.add(product);
}
} 2. Filtering and Iterating Collection using Stream:
In this code snippet, the same filtering functionality is achieved using Java 8 Streams. The filter() operation is applied to the stream, and the resulting elements are iterated using the forEach() method.
List productsList = new ArrayList();
// Adding Products...
List filteredProducts = productsList.stream()
.filter(product -> product.getPrice() < 30000)
.collect(Collectors.toList()); 3. Iterating with Stream and limit():
This code example demonstrates how to iterate over a stream of numbers, filter them based on a condition, and limit the results to a specific count using the limit() operation.
Stream.iterate(1, element -> element + 1)
.filter(element -> element % 5 == 0)
.limit(5)
.forEach(System.out::println);These examples illustrate different ways of filtering and iterating collections, both with and without the use of Java 8 Streams. By leveraging Streams, you can write more concise and expressive code that simplifies data manipulation and enhances readability.
Conclusion
Java 8 Streams revolutionized the way we process data in Java by providing a functional and declarative approach. They enable concise and expressive code, efficient parallel processing, and lazy evaluation. Understanding the key concepts and functionalities of Java 8 Streams empowers developers to write clean and efficient code, simplifying complex data processing tasks and unleashing the full potential of Java. By embracing Streams, you can elevate your Java development to a new level of elegance and efficiency.
Frequently Asked Questions (FAQs)
Here are some of the most frequently asked questions related to Java 8 stream
1. What is the Java 8 Stream?
Java 8 Stream is an API introduced in Java 8 that provides a sequence of elements for processing collections of data in a declarative and functional style. It offers operations to perform computations on the data, such as filtering, mapping, reducing, and more.
2. What are the Stream types in Java 8?
In Java 8, there are three types of streams provided by the Stream API: Stream<T> for objects of type T, IntStream for primitive integers, and LongStream for primitive long values. Additionally, there is DoubleStream for primitive double values.
3. Why is the Java Stream used?
Java Stream is used to simplify and enhance the processing of collections in Java. It allows developers to write code in a more concise and readable manner, abstracting away the complexities of iteration. Streams also enable efficient parallel processing of large data sets, resulting in improved performance.
4. What are Lambda and Stream in Java 8?
A: In Java 8, Lambda expressions are anonymous functions that allow the representation of methods as concise blocks of code. Streams, on the other hand, are a sequence of elements that can be processed in parallel or sequentially. Lambdas are often used in conjunction with Streams to provide a functional programming style for data processing.
5. How many streams are there in Java?
In Java, there are four types of streams available: Stream<T> for objects, IntStream for integers, LongStream for long values, and DoubleStream for double values. Each stream type provides specialized operations for efficient processing and can be processed in parallel to leverage multi-core processors.