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Streams intermediate

Stream.iterate() with predicate

Use a predicate to stop iteration — like a for-loop in stream form.

Code Comparison
✕ 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
Why the modern way wins
🎯

Natural termination

Stop based on a condition, not an arbitrary limit.

📐

For-loop equivalent

Same semantics as for(seed; hasNext; next).

🛡️

No infinite stream risk

The predicate guarantees termination.

Old Approach
iterate + limit
Modern Approach
iterate(seed, pred, op)
Since JDK
9
Difficulty
intermediate
JDK Support
Stream.iterate() with predicate
Available

Widely available since JDK 9 (Sept 2017)

How it works

The three-argument Stream.iterate(seed, hasNext, next) works like a for-loop: seed is the start, hasNext determines when to stop, and next produces the next value.

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 intermediate

Optional.or() fallback

Java 8
Optional<Config> cfg = primary();
if (!cfg.isPresent()) {
    cfg = secondary();
}
if (!cfg.isPresent()) {
    cfg = defaults();
}
Java 9+
Optional<Config> cfg = primary()
    .or(this::secondary)
    .or(this::defaults);
Hover to see modern ➜
JDK 9+ →
Streams beginner

Optional.ifPresentOrElse()

Java 8
Optional<User> user = findUser(id);
if (user.isPresent()) {
    greet(user.get());
} else {
    handleMissing();
}
Java 9+
findUser(id).ifPresentOrElse(
    this::greet,
    this::handleMissing
);
Hover to see modern ➜
JDK 9+ →
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