The Stream API is one of the prominent features introduced in Java 8, designed to simplify and enhance the way developers work with sequences of data (such as collections or arrays). The Stream API facilitates a more functional and declarative approach to data manipulation, allowing developers to express complex operations on data in a concise and readable manner.
Streams in Java are not data structures, but rather a sequence of elements that can be processed sequentially or in parallel. They provide a way to perform operations on data without modifying the underlying data source, promoting immutability and enhancing code quality. The Stream API encourages developers to focus on what needs to be done (functional programming) rather than how it should be done (imperative programming).
Key Characteristics of Streams:
1. Sequence of Elements: Streams represent a sequence of elements, which can be of any data type such as integers, objects, or even custom classes.
2. Functional Operations: Streams provide a set of functional operations that can be performed on data, including filtering, mapping, sorting, and reducing.
3. Lazy Evaluation: Streams support lazy evaluation, meaning that operations are not executed until a terminal operation is invoked. This improves performance by avoiding unnecessary computations.
4. Pipelining: You can chain multiple stream operations together (method chaining), creating a pipeline of operations that are executed sequentially.
5. Parallel Processing: Streams can be processed in parallel, utilizing multiple cores of the CPU for improved performance on large datasets.
Common Stream Operations:
1. filter(): Returns a new stream with elements that satisfy a given predicate.
2. map(): Transforms each element in the stream using a given function.
3. flatMap(): Transforms each element in the stream into a stream of other elements, then flattens the result into a single stream.
4. sorted(): Returns a new stream with elements sorted based on a specified comparator.
5. distinct(): Returns a new stream with distinct elements (removing duplicates).
6. limit(): Returns a new stream with the first N elements.
7. skip(): Returns a new stream with elements after skipping the first N elements.
8. reduce(): Performs a reduction operation on the elements using a specified binary operator.
9. collect(): Aggregates the elements of the stream into a collection or other data structure.
10. forEach(): Applies an action to each element of the stream.
Example Usage of the Stream API:
Suppose you have a list of integers and you want to filter out the even numbers, double them, and then find their sum:
List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
int sumOfEvenDoubles = numbers.stream()
.filter(num -> num % 2 == 0)
.mapToInt(num -> num * 2)
.sum();
System.out.println("Sum of even doubles: " + sumOfEvenDoubles);
In this example, the Stream API is used to create a stream from the list of numbers, filter out even numbers, double them using `mapToInt()`, and finally compute the sum using `sum()`.
The Stream API in Java 8 enables developers to write more expressive and concise code for data manipulation, improving code readability and maintainability. It promotes functional programming paradigms and provides a powerful tool for working with collections and arrays.