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Streams beginner

Stream.toList()

Terminal toList() replaces the verbose collect(Collectors.toList()).

Code Comparison
✕ Java 8 
List<String> result = stream
    .filter(s -> s.length() > 3)
    .collect(Collectors.toList());
✓ Java 16+ 
List<String> result = stream
    .filter(s -> s.length() > 3)
    .toList();
Why the modern way wins
📏

7 chars vs 24

.toList() replaces .collect(Collectors.toList()).

🔒

Immutable

The result list cannot be modified.

📖

Fluent

Reads naturally at the end of a pipeline.

Old Approach
Collectors.toList()
Modern Approach
.toList()
Since JDK
16
Difficulty
beginner
JDK Support
Stream.toList()
Available

Widely available since JDK 16 (March 2021)

How it works

Stream.toList() returns an unmodifiable list. It's equivalent to .collect(Collectors.toUnmodifiableList()) but much shorter. Note: the result is immutable, unlike Collectors.toList().

Related patterns

Streams intermediate

Virtual thread executor

Java 8
ExecutorService exec =
    Executors.newFixedThreadPool(10);
try {
    futures = tasks.stream()
        .map(t -> exec.submit(t))
        .toList();
} finally {
    exec.shutdown();
}
Java 21+
try (var exec = Executors
        .newVirtualThreadPerTaskExecutor()) {
    var futures = tasks.stream()
        .map(exec::submit)
        .toList();
}
Hover to see modern ➜
JDK 21+ →
Streams advanced

Stream gatherers

Java 8
// Sliding window: manual implementation
List<List<T>> windows = new ArrayList<>();
for (int i = 0; i <= list.size()-3; i++) {
    windows.add(
        list.subList(i, i + 3));
}
Java 24+
var windows = stream
    .gather(
        Gatherers.windowSliding(3)
    )
    .toList();
Hover to see modern ➜
JDK 24+ →
Streams intermediate

Stream.iterate() with predicate

Java 8
Stream.iterate(1, n -> n * 2)
    .limit(10)
    .forEach(System.out::println);
// can't stop at a condition
Java 9+
Stream.iterate(
    1,
    n -> n < 1000,
    n -> n * 2
).forEach(System.out::println);
// stops when n >= 1000
Hover to see modern ➜
JDK 9+ →
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