All 32 Java Stream Methods with Examples

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 Java Streams, introduced in Java 8, bring a functional programming flavor to Java by allowing you to process collections of data in a declarative and concise manner. A stream represents a sequence of elements supporting sequential and parallel operations.

Unlike collections, a stream does not store data. Instead, it conveys elements from a source such as a collection, an array, or an I/O channel through a pipeline of computational operations.

Think of streams as data pipelines where each element flows through a series of transformations (intermediate operations) and ends in a result (terminal operation).

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Key Characteristics of Java Streams

• Declarative: Describe what you want to do, not how.
• Lazy Evaluation: Intermediate operations are only executed when a terminal operation is triggered.
• No Side Effects: Stream operations should not mutate the underlying source.

In this article, we cover every method available in the java.util.stream.Stream interface, categorized by:

• Creation Methods
• Intermediate Operations
• Terminal Operations
• Utility Methods

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🔄 Stream Creation Methods

1. Stream.of(...)

Creates a stream from values.

Stream<String> stream = Stream.of("Java", "Python", "Kotlin");

2. Stream.empty()

Returns an empty stream.

Stream<String> empty = Stream.empty();

3. Stream.generate(Supplier)

Generates an infinite stream using a Supplier.

Stream<Double> randoms = Stream.generate(Math::random).limit(5);

4. Stream.iterate(...)

Generates an infinite stream by iterative function.

Stream<Integer> evens = Stream.iterate(0, n -> n + 2).limit(5);

5. Collection.stream()

Creates a stream from a collection.

List<String> list = List.of("A", "B", "C");
Stream<String> stream = list.stream();

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🧹 Intermediate Operations (Lazy)

These return a new stream and are lazy (executed only when a terminal operation is triggered).

6. filter(Predicate)

Filters elements based on a condition.

list.stream().filter(s -> s.startsWith("A"))

7. map(Function)

Transforms elements.

list.stream().map(String::toUpperCase)

8. flatMap(Function)

Flattens nested streams.

Stream<List<String>> listOfLists = ...;
listOfLists.flatMap(List::stream)

9. distinct()

Removes duplicate elements.

list.stream().distinct()

10. sorted()

Sorts elements naturally.

list.stream().sorted()

11. sorted(Comparator)

Sorts elements using a custom comparator.

list.stream().sorted(Comparator.reverseOrder())

12. peek(Consumer)

Allows debugging by peeking each element.

list.stream().peek(System.out::println)

13. limit(long n)

Limits the number of elements.

list.stream().limit(3)

14. skip(long n)

Skips the first n elements.

list.stream().skip(2)

15. takeWhile(Predicate) (Java 9+)

Takes elements while the condition is true.

list.stream().takeWhile(s -> s.length() < 5)

16. dropWhile(Predicate) (Java 9+)

Skips elements while condition is true.

list.stream().dropWhile(s -> s.length() < 5)

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🚦 Terminal Operations (Eager)

These trigger the execution of the stream pipeline.

17. forEach(Consumer)

Performs an action on each element.

list.stream().forEach(System.out::println);

18. forEachOrdered(Consumer)

Processes elements in encounter order.

list.parallelStream().forEachOrdered(System.out::println);

19. toArray()

Converts stream to an array.

String[] array = list.stream().toArray(String[]::new);

20. reduce(...)

Reduces the elements into one using an accumulator.

int sum = list.stream().reduce(0, Integer::sum);

21. collect(Collector)

Collects elements into a collection or summary.

List<String> collected = list.stream().collect(Collectors.toList());

22. min(Comparator)

Finds the minimum element.

Optional<String> min = list.stream().min(Comparator.naturalOrder());

23. max(Comparator)

Finds the maximum element.

Optional<String> max = list.stream().max(Comparator.naturalOrder());

24. count()

Counts the number of elements.

long count = list.stream().count();

25. anyMatch(Predicate)

Returns true if any element matches.

boolean hasA = list.stream().anyMatch(s -> s.startsWith("A"));

26. allMatch(Predicate)

Returns true if all elements match.

boolean allShort = list.stream().allMatch(s -> s.length() < 10);

27. noneMatch(Predicate)

Returns true if no elements match.

boolean noneEmpty = list.stream().noneMatch(String::isEmpty);

28. findFirst()

Returns the first element.

Optional<String> first = list.stream().findFirst();

29. findAny()

Returns any element (useful in parallel streams).

Optional<String> any = list.stream().findAny();

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🛠️ Utility Methods

30. builder()

Used to build a stream manually.

Stream<String> stream = Stream.<String>builder().add("A").add("B").build();

31. concat(Stream, Stream)

Concatenates two streams.

Stream<String> combined = Stream.concat(stream1, stream2);

32. ofNullable(T) (Java 9+)

Creates a stream of one element or empty if null.

Stream<String> maybe = Stream.ofNullable(possibleNull);

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Final Thoughts

Java Streams simplify collection processing by enabling fluent, functional-style operations. Mastering each method helps you write concise, powerful, and readable code.

Use this article as your go-to reference when working with Java Streams!

References

📚 Java Stream API — From Beginner to Pro in One Ultimate Guide
This is the Ultimate Guide to learn everything about Java Stream API with examples, real-world use cases and best…rameshfadatare.medium.com

Java Stream Collectors Deep Dive (With Real-World Examples)
Java Stream Collectors are one of the most powerful features in the Stream API. They help you gather, group, join, or…medium.com

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