25_Stream_API.md

Stream API

What is the Stream API?

• It abstracts data to provide a common way to read and write data stored in various ways
  • Using the Stream API, not only arrays and Collections but also data stored in files can all be handled in the same way
• It is a feature that allows stored elements of arrays, lists, and other collections to be referenced one by one and processed with lambda expressions
• It is needed when implementing sorting, filtering, duplicate removal, etc. of data within a Collection

Characteristics of Streams

• Unlike collections that operate through external iteration, Streams operate through internal iteration
• Streams are single-use
  • Unlike Collections which are reusable, once a Stream is used it is closed and cannot be reused
  • If needed, sorted results can be stored in a Collection or array and returned
• Streams do not modify the original data
  • Streams only read data from the original data and do not modify the original data itself
• Stream operations use filter-map based APIs to optimize performance through lazy evaluation
• Streams support easy parallel processing through the parallelStream() method
• Streams process work through internal iteration
  • One of the reasons Stream-based work can be concise is internal iteration
  • Internal iteration means that loops can be hidden inside methods
    • Loops are not exposed in the code

Stream API Operation Flow

1. Creation of the Stream
2. Intermediate operations of the Stream (transformation of the Stream)
3. Terminal operations of the Stream (consumption of the Stream)