Java streams are a feature introduced in Java 8 that allows developers to perform functional-style operations on collections of data. Streams are designed to make it easier to write more concise, declarative code for manipulating collections, and to take advantage of multi-core processors for improved performance.
A Java stream is a sequence of elements that can be processed in a pipeline. The pipeline consists of one or more operations that are executed on the stream in a specific order. There are two types of operations: intermediate operations and terminal operations.
Intermediate operations are operations that transform the stream into another stream. Some examples of intermediate operations include filter, map, and sorted. These operations are lazy, which means that they don’t actually perform any computation until a terminal operation is called.
Terminal operations are operations that produce a result or a side-effect. Some examples of terminal operations include forEach, reduce, and collect. Terminal operations are what trigger the computation of the pipeline, and once a terminal operation is called, the stream can no longer be used.
Here’s an example of how streams work:
List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5); int sum = numbers.stream() .filter(n -> n % 2 == 0) .mapToInt(n -> n * 2) .sum(); System.out.println(sum);
In this example, we have a list of numbers and we want to sum the values of the even numbers, multiplied by 2. We create a stream from the list, use the
filter operation to keep only the even numbers, use the
mapToInt operation to multiply each even number by 2 and convert it to an
int, and then use the
sum operation to add up all the resulting values. The final result is printed to the console.
Important Features in Java Stream
Java streams have several important features that make them a powerful tool for working with collections of data. Here are some of the most important features of Java streams:
- Stream pipeline operations: Java streams support a variety of pipeline operations that allow you to process collections of data in a concise and functional style. Some of the most commonly used pipeline operations include
- Lazy evaluation: One of the key features of Java streams is their support for lazy evaluation. This means that intermediate operations on a stream are not evaluated until a terminal operation is invoked. This allows you to chain multiple intermediate operations together without incurring any performance penalty until you actually need the final result.
- Parallel processing: Another key feature of Java streams is their support for parallel processing. This allows you to take advantage of multi-core processors to process collections of data more quickly. By default, streams use the available number of processor cores to parallelize the processing of the data.
- Functional programming: Java streams are designed to support functional programming concepts like higher-order functions, lambda expressions, and method references. This allows you to write concise, expressive code that is easier to read and maintain.
- Reduced code complexity: By using streams, you can often reduce the amount of code needed to process collections of data. This can make your code more readable and less error-prone.
- Backed by existing collection classes: Java streams are built on top of the existing collection classes in Java, which means that they are familiar and easy to use for developers who are already familiar with Java collections.
Important Classes in Java Stream
here are some of the most important classes in Java streams:
- Stream: The Stream class is the main entry point for working with Java streams. It represents a sequence of elements that can be processed in a pipeline of operations.
- Collectors: The Collectors class provides a set of predefined collectors that can be used to accumulate the elements of a stream into a collection or other type of object. For example, the
toList()collector can be used to collect the elements of a stream into a list.
- Optional: The Optional class is used to represent the possibility of a null value. It can be used in stream pipelines to avoid null pointer exceptions and to provide a more functional way of dealing with missing values.
- IntStream, LongStream, and DoubleStream: These classes represent streams of primitive types
double, respectively. They provide a more efficient way of processing streams of primitive values than using the generic Stream class.
- Stream.Builder: The Stream.Builder class is used to create a stream from a sequence of elements. It can be useful when you need to create a stream from a collection that does not already have a
- StreamSupport: The StreamSupport class provides utility methods for creating and working with streams that are backed by other data structures, such as arrays or iterators.
- BaseStream: The BaseStream class is the base interface for all streams in Java. It defines a common set of methods that are shared by all types of streams.
These are just a few of the most important classes in Java streams. There are many other classes and interfaces in the Java stream API that provide additional functionality and customization options.