Streams

A stream pipeline consists of a source, zero or more intermediate operations, and a terminal operation.

Basic pipeline

List<String> result = words.stream()
        .filter(word -> word.length() >= 4)
        .map(String::toUpperCase)
        .sorted()
        .toList();

filter, map, and sorted are intermediate operations. toList is terminal.

Laziness

Intermediate operations are lazy: they describe work but do not normally execute it until a terminal operation requests results.

long count = words.stream()
        .filter(StringUtils::isPalindrome)
        .count();

Reduction

int total = numbers.stream()
        .mapToInt(Integer::intValue)
        .sum();

Optional<Integer> maximum = numbers.stream()
        .max(Integer::compareTo);

Collecting

Map<Integer, List<String>> byLength = words.stream()
        .collect(Collectors.groupingBy(String::length));

Streams are single-use

After a terminal operation, create a new stream rather than attempting to reuse the old one.

Parallel streams

Parallel execution is not automatically faster. Use it only for suitable, measurable, stateless workloads where ordering and shared mutable state are handled correctly.

Repository examples

• src/main/java/nitin/streams
• src/main/java/nitin/io/fileIO/readfiles1
• src/main/java/nitin/io/fileIO/readfiles2
• src/main/java/nitin/io/fileIO/readfiles3