collecting data with streams

Collecting is the terminal phase of a stream pipeline where processed elements are accumulated into a final result. While intermediate operations like filtering and mapping transform the data, collectors define how that transformed data is gathered—whether into collections, maps, summary statistics, or grouped structures. The Collectors utility class provides a rich set of predefined collectors for common aggregation tasks such as summing values, generating summary statistics, grouping elements by a key, and partitioning data based on a condition. These operations allow complex data transformations to be expressed in a clear and declarative manner without manual iteration or mutable state. The articles in this section explore the Collectors API in detail, covering basic collectors as well as advanced grouping and partitioning techniques, helping you confidently collect and shape stream results in real-world Java applications.