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}

"".isEmpty();      // true
"   ".isEmpty();   // false

"".isBlank();      // true
"   ".isBlank();   // true
"\n\t".isBlank();  // true

if (name == null || name.isBlank()) {
    name = "Guest";
}

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