Streams API in Java

From the Java cheat sheet · Streams & Optional · verified Jul 2026

Transform and aggregate collections functionally.

java

// Quick Reference
list.stream()
    .filter(x -> x > 2)
    .map(x -> x * 10)
    .toList();

💡 Streams are lazy - nothing runs until a terminal operation like toList() or count().

⚡ .toList() (Java 16+) is the concise replacement for .collect(Collectors.toList()).

📌 Use mapToInt/mapToDouble for numeric streams with sum(), average(), and range helpers.

🟢 A stream is single-use; create a fresh one for each pipeline you run.

streamsfunctional

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