Java 8 stream is a powerful feature of the Java programming language that allow you to process collections of data in a declarative and functional style. In this tutorial, we will take a look at the basics of Java streams and how to use them to manipulate collections of data in your Java code.
Before we dive into Java streams, it’s important to understand that streams are designed to process data in a “lazy” and “pipelined” fashion. This means that streams do not actually store the data they are processing. Instead, they operate on the data as it is needed, and they pass the results of their operations to the next stage in the stream pipeline. This allows streams to be very efficient and performant, as they only process the data that is needed and do not store unnecessary data in memory.
To create a Java stream, you can use the
stream() method of the
Collection interface. This method returns a
Stream object that you can use to perform operations on the elements of the collection. Here is an example of how to create a stream from a list:
List<String> list = Arrays.asList("apple", "banana", "orange"); Stream<String> stream = list.stream();
Once you have a stream, you can use various stream methods to perform operations on the elements of the stream. For example, you can use the
map() method to transform the elements of the stream, the
filter() method to select only certain elements, and the
reduce() method to combine the elements in some way. Here is an example of how you might use these methods to transform a stream of strings:
List<String> list = Arrays.asList("apple", "banana", "orange"); Stream<String> stream = list.stream(); // Transform the elements of the stream Stream<String> transformedStream = stream.map(s -> s.toUpperCase()); // Select only certain elements Stream<String> filteredStream = transformedStream.filter(s -> s.startsWith("A")); // Combine the elements of the stream Optional<String> reduced = filteredStream.reduce((s1, s2) -> s1 + "," + s2); // Print the result System.out.println(reduced.orElse(""));
This code will create a stream from the list of strings, transform the elements of the stream by converting them to uppercase, filter out any elements that do not start with the letter “A”, and then reduce the elements of the stream to a single string by concatenating them together with commas. The result of this operation will be printed to the console.
There are many other stream methods that you can use to perform various operations on streams. Some of the most commonly used methods include
collect(). You can also use the
parallelStream() method to create a stream that can be processed in parallel, which can be useful for improving the performance of certain operations on large collections of data.
Overall, Java streams are a powerful and convenient way to manipulate collections of data in a functional style. By using stream methods, you can easily transform, filter, and reduce collections of data in a concise and efficient manner.