.filter(name -> !name.isBlank())

.filter(Predicate.not(String::isBlank))

List<String> names = users.stream()
        .map(User::name)
        .filter(Objects::nonNull)
        .filter(Predicate.not(String::isBlank))
        .toList();

Predicate.not(String::isEmpty)
Predicate.not(Collection::isEmpty)
Predicate.not(Optional::isEmpty)

Оставляю ссылочку: GitHub 📱

record Task(String title, boolean done) {}

List<Task> tasks = List.of(
        new Task("Read docs", false),
        new Task("Write tests", true),
        new Task("Fix bug", false)
);

List<Task> active = new ArrayList<>();

for (Task task : tasks) {
    if (!task.done()) {
        active.add(task);
    }
}

List<Task> active = tasks.stream()
        .filter(task -> !task.done())
        .toList();

active.forEach(System.out::println);

Task[title=Read docs, done=false]
Task[title=Fix bug, done=false]

List<Order> paid = orders.stream()
        .filter(Order::isPaid)
        .toList();

String json = "{\n" +
        "  \"name\": \"" + name + "\",\n" +
        "  \"active\": true\n" +
        "}";

String json = """
        {
          "name": "%s",
          "active": true
        }
        """.formatted(name);

String sql = """
        SELECT id, email, created_at
        FROM users
        WHERE active = true
        ORDER BY created_at DESC
        """;

String message = """
        Hello, %s!
        Your order #%d is ready.
        """.formatted(name, orderId);

Оставляю ссылочку: GitHub 📱

String name = user.name();

if (name == null) {
    name = "Guest";
}

String name = Objects.requireNonNullElse(
    user.name(),
    "Guest"
);

String name = Objects.requireNonNullElseGet(
    user.name(),
    () -> loadDefaultName()
);

record LogEntry(String level, String message) {}
Подготовим данные:

List<LogEntry> logs = List.of(
        new LogEntry("INFO", "User opened page"),
        new LogEntry("ERROR", "Payment failed"),
        new LogEntry("WARN", "Slow response"),
        new LogEntry("ERROR", "Database timeout")
);

List<String> result = new ArrayList<>();

for (LogEntry log : logs) {
    if (log.level().equals("ERROR")) {
        result.add(log.message());
    }
}

List<String> result = logs.stream()
        .filter(log -> log.level().equals("ERROR"))
        .map(LogEntry::message)
        .toList();

[Payment failed, Database timeout]

List<String> words = List.of(
    "java", "spring", "java", "api", "spring", "java"
);

Map<String, Long> result = new HashMap<>();

for (String word : words) {
    result.put(word, result.getOrDefault(word, 0L) + 1);
}

Map<String, Long> result = words.stream()
    .collect(Collectors.groupingBy(
        Function.identity(),
        Collectors.counting()
    ));

{spring=2, java=3, api=1}