Process collections of data in a declarative, functional style.
The Streams API, introduced in Java 8, provides a powerful and declarative way to process sequences of data. A stream is not a data structure that stores elements; instead, it's a sequence of elements from a source (like a `Collection`, an array, or an I/O channel) that supports aggregate operations. Stream operations are divided into two categories: intermediate and terminal. Intermediate operations, such as `filter()` (selects elements based on a predicate), `map()` (transforms each element), and `sorted()`, return a new stream. This allows you to chain multiple operations together to form a processing pipeline. These operations are lazy, meaning they are not executed until a terminal operation is invoked. Terminal operations, such as `forEach()` (performs an action for each element), `collect()` (gathers the stream elements into a collection), or `reduce()` (combines all elements into a single result), produce a result or a side-effect. Once a terminal operation is executed, the stream is considered consumed and cannot be reused. This functional approach to data processing often leads to more readable and concise code compared to traditional imperative loops. For example, to find all transactions of a certain type, sort them by value, and collect their IDs into a list, you can create a simple, elegant pipeline of stream operations. The Streams API also supports parallel processing. By simply calling `.parallelStream()` instead of `.stream()`, the framework can automatically process the data in parallel on multi-core processors, potentially offering significant performance improvements.