Java Streams Cheatsheet

February 11, 2025 java,, programming

A quick reference for common Java Stream operations.

Creating Streams

List<String> list = Arrays.asList("a", "b", "c");
Stream<String> s1 = list.stream();

String[] arr = {"x", "y", "z"};
Stream<String> s2 = Arrays.stream(arr);

Stream<Integer> s3 = Stream.of(1, 2, 3);

Common Operations

Operation	Purpose
`filter(predicate)`	Keep elements matching predicate
`map(function)`	Transform each element
`flatMap(function)`	Flatten nested structures
`sorted()`	Sort (natural order)
`distinct()`	Remove duplicates
`limit(n)`	Take first n elements
`skip(n)`	Skip first n elements

Collectors

List<String> list = stream.collect(Collectors.toList());
Set<String> set = stream.collect(Collectors.toSet());
String joined = stream.collect(Collectors.joining(", "));
Map<K, V> map = stream.collect(Collectors.toMap(k -> k, v -> v));

Example: Filter and Map

List<String> result = names.stream()
    .filter(n -> n.length() > 3)
    .map(String::toUpperCase)
    .collect(Collectors.toList());