Java Streams Collector Operations Explained with Examples
Collectors are the workhorses of Stream terminal aggregation in Java 8. They let you join strings, group and partition data, build specific collection types, and compute statistics — all in a fluent, readable style. 1) Collectors.joining() — Concatenate elements Concatenate stream elements into a single string with optional delimiter, prefix, and suffix. List<String> words = Arrays.asList("apple", "banana", "cherry"); String joined = words.stream() .collect(Collectors.joining(", ", "[", "]")); System.out.println(joined); // [apple, banana, cherry] 2) Collectors.groupingBy() — Group by classifier Group elements based on a key extractor. Default downstream is toList() . List<Person> people = Arrays.asList( new Person("John", "New York"), new Person("Wick", "London"), new Person("Smith", "New York") ); Map...