Collectors in java8 streams

 

Java 8’s Collectors class provides a suite of static methods for accumulating elements from a stream into collections, strings, maps, and more.

 Collectors are typically used with the Stream.collect() method, making it easy to process and transform data in a functional style.

Why:

Collectors provide ready-made solutions for common reduction operations, such as collecting stream elements into collections, grouping, partitioning, joining, and summarizing data. They make code concise, readable, and expressive.

When:

Use collectors when you want to gather, transform, group, or summarize data from a stream into a desired result format (e.g., List, Set, Map, or a single value).

Common Collectors and Their Use Cases

1. Collectors.toList()

When: 

When you want to collect stream elements into a List.

Example:

List<String> cities = Arrays.asList("Mumbai", "Delhi", "Bangalore", "Chennai");

List<String> cityList = cities.stream().collect(Collectors.toList());

System.out.println(cityList); // Output: [Mumbai, Delhi, Bangalore, Chennai]

Explanation:

Collects all stream elements into a List in encounter order

2. Collectors.toSet()

When:

When you need a Set (no duplicates) from stream elements.

Example:

List<String> cities = Arrays.asList("Mumbai", "Delhi", "Mumbai", "Bangalore");

Set<String> citySet = cities.stream().collect(Collectors.toSet());

System.out.println(citySet); // Output: [Mumbai, Delhi, Bangalore]

Explanation:

Removes duplicates by collecting elements into a Set