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Stream API
Last Updated : 26 May, 2026
title: Stream API in Java 8
Java 8 Features50 words5 headingsExamples included
title: Stream API in Java 8 description: Java 8 Stream API ka complete guide
Collection processing ka functional style. Lazy evaluation, chaining possible.
Stream kya hai?
Data elements ki pipeline. Source → Intermediate operations → Terminal operation.
java exampleWoHoTech
List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
// Stream pipeline
int sum = numbers.stream() // Source
.filter(n -> n % 2 == 0) // Intermediate: Even numbers
.mapToInt(Integer::intValue) // Intermediate: Integer to int
.sum(); // Terminal: Sum
System.out.println("Sum of evens: " + sum); // 30Stream Create karna
java exampleWoHoTech
// Collection se
List<String> list = Arrays.asList("a", "b", "c");
Stream<String> s1 = list.stream();
Stream<String> s2 = list.parallelStream(); // Parallel processing
// Array se
Stream<Integer> s3 = Arrays.stream(new Integer[]{1, 2, 3});
// Static factory
Stream<String> s4 = Stream.of("x", "y", "z");
Stream<Integer> s5 = Stream.iterate(0, n -> n + 2).limit(5); // 0,2,4,6,8
Stream<Double> s6 = Stream.generate(Math::random).limit(3);Intermediate Operations (Lazy)
java exampleWoHoTech
List<String> names = Arrays.asList("Ram", "Shyam", "Geeta", "Rita", "Mohan");
// filter — condition match karo
names.stream().filter(s -> s.length() > 3) // Shyam, Geeta, Rita, Mohan
// map — transform each element
names.stream().map(String::toUpperCase) // RAM, SHYAM, ...
names.stream().map(String::length) // 3, 5, 5, 4, 5
// flatMap — flatten nested streams
List<List<Integer>> nested = Arrays.asList(Arrays.asList(1,2), Arrays.asList(3,4));
nested.stream().flatMap(Collection::stream) // 1, 2, 3, 4
// distinct — unique elements
Stream.of(1,2,2,3,3,3).distinct() // 1, 2, 3
// sorted — sort karo
names.stream().sorted() // Alphabetical
names.stream().sorted(Comparator.reverseOrder())
// limit / skip
names.stream().limit(3) // First 3
names.stream().skip(2) // Skip first 2
// peek — side effect (debugging)
names.stream().peek(System.out::println).filter(s -> s.length() > 3)Terminal Operations (Eager)
java exampleWoHoTech
// collect
List<String> result = names.stream().filter(s -> s.startsWith("R")).collect(Collectors.toList());
Set<String> set = names.stream().collect(Collectors.toSet());
String joined = names.stream().collect(Collectors.joining(", ")); // "Ram, Shyam, ..."
Map<Integer, List<String>> byLength = names.stream().collect(Collectors.groupingBy(String::length));
// forEach
names.stream().forEach(System.out::println);
// count
long count = names.stream().filter(s -> s.length() > 3).count();
// findFirst / findAny
Optional<String> first = names.stream().filter(s -> s.startsWith("R")).findFirst();
// anyMatch / allMatch / noneMatch
boolean anyR = names.stream().anyMatch(s -> s.startsWith("R")); // true
boolean allLong = names.stream().allMatch(s -> s.length() > 2); // true
// reduce
int sum = Stream.of(1,2,3,4,5).reduce(0, Integer::sum); // 15
Optional<Integer> max = Stream.of(3,1,4,1,5).reduce(Integer::max);
// min / max
Optional<String> shortest = names.stream().min(Comparator.comparingInt(String::length));
// toArray
Object[] arr = names.stream().toArray();
String[] strArr = names.stream().toArray(String[]::new);Primitive Streams
java exampleWoHoTech
IntStream.range(1, 6) // 1,2,3,4,5
IntStream.rangeClosed(1, 5) // 1,2,3,4,5
IntStream.of(1,2,3).sum() // 6
IntStream.of(1,2,3).average() // OptionalDouble
// int to Integer
IntStream.range(1,6).boxed() // Stream<Integer>
// Integer to int
Stream.of(1,2,3).mapToInt(Integer::intValue).sum()Exam Focus
Revise definitions, diagrams, examples, and short-answer points for Stream API.
Interview Use
Prepare one clear explanation, one practical example, and one common mistake for this Java topic.
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