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Java Streams

Java Stream Introduction

A stream is a sequence of data values supporting sequential and parallel aggregate operations.

• Using aggregate functions we can sum all sales figures for a month, region or product.
• Aggregate operations work on a list of items and produces a single value.
• The result of an aggregate operation on stream may be primative value, an object or a void for Stream.

Collections Vs Streams

Collections

• Java Collections focus on how to store data elements for efficient access.

Storage

Java Collection is an in-memory data structure that stores all its elements.

Infinite Streams

Java Collection cannot reprsent a group of infinate elements

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Streams

• Java Streams focus on aggregate operations on data elements from a data source.

Storage

Java Streams has no storage.
Java stream pulls elements from a data source on-demand and passes them to a pipeline of operations for processing.
Java Streams we focus on operations Example (Aggregates)

Infinite Streams

Java Streams can reprsent a group of infinate elements
Java Streams can pull its elements from data source. The data sourse can be a collection, a function that generates data, an I/O channel, etc.
A Java Stream can pull data from a function which generates infinate number of elements.

Reusability

Java Streams cannot be reusable after calling a teriminal operation.
To perform a computation on the same elements from the data source, we have to recrete the stream pipeline.
Java Streams can throw an illegalStateException in case of reusing

Stream Operation

Internal Iteration

Parallel

use parallelStream() instead stream()
Easy to use when using internal iteration provided by stream.

Intermediate Operations

Intermediate operation is also called lazy operations.
Intermediate operation on a stream produces another stream.
filter(), map() are lazy operations.

Terminal Operations

Terminal operations are also called eager operations
reduce() is a eager operation.