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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Map<Long, String> usersById = users.stream()
        .collect(Collectors.toMap(User::id, User::name));

IllegalStateException: Duplicate key

Map<Long, String> usersById = users.stream()
        .collect(Collectors.toMap(
                User::id,
                User::name,
                (oldName, newName) -> newName
        ));

(oldName, newName) -> oldName

record Product(String name, BigDecimal price) {}

List<Product> products = List.of(
        new Product("Keyboard", new BigDecimal("79.99")),
        new Product("Mouse", new BigDecimal("39.99")),
        new Product("Monitor", new BigDecimal("249.99"))
);

Product top = products.get(0);
for (Product product : products) {
    if (product.price().compareTo(top.price()) > 0) {
        top = product;
    }
}

Optional<Product> top = products.stream()
        .max(Comparator.comparing(Product::price));

Product product = top.orElseThrow();