Java asoslari 9-qism. Java 8+

Java 8+ features — Java’ni eski “faqat OOP” uslubidan zamonaviy, qisqa, funksional va qulay yozish uslubiga olib chiqqan imkoniyatlar.

Bu bo‘limga quyidagilar kiradi: Lambda expressions, Functional interfaces, Stream API, Optional, Method references, Default & static interface methods, Date/Time API (java.time).

1. Java 8 nega muhim?

Java 8’dan oldin ko‘p kodlar juda uzun yozilardi.

Masalan, ro‘yxatdagi ismlarni chiqarish:

List<String> names = List.of("Ali", "Vali", "Hasan");

for (String name : names) {
    System.out.println(name);
}

Java 8’dan keyin buni qisqaroq yozish mumkin:

names.forEach(name -> System.out.println(name));

Yoki yanada qisqa:

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

Java 8+ sizga quyidagilarni beradi:

• kamroq boilerplate kod;

• collectionlar bilan qulay ishlash;

• filter, map, sort, group qilish;

• null bilan xavfsizroq ishlash;

• vaqt/sana bilan to‘g‘ri ishlash;

• funksional programming elementlari.

2. Lambda Expression

Lambda — methodni qisqa ko‘rinishda yozish usuli.

Oddiy ko‘rinishi:

(parameter) -> action

Masalan:

name -> System.out.println(name)

Bu degani:

name degan qiymat keladi, uni print qilamiz

2.1 Lambda oldidan qanday yozilardi?

Java 8’dan oldin anonymous class ishlatilardi.

Runnable task = new Runnable() {
    @Override
    public void run() {
        System.out.println("Task ishladi");
    }
};

Java 8 bilan:

Runnable task = () -> System.out.println("Task ishladi");

Bu yerda:

• () — parameter yo‘q;

• -> — lambda belgisi;

• System.out.println(...) — bajariladigan ish.

2.2 Lambda misollar

Bitta parameter

Consumer<String> printer = name -> System.out.println(name);

printer.accept("Ali");

Ikkita parameter

BiFunction<Integer, Integer, Integer> sum = (a, b) -> a + b;

System.out.println(sum.apply(10, 20));

Natija:

30

Bir nechta qatorli lambda

Consumer<String> printer = name -> {
    System.out.println("Name:");
    System.out.println(name);
};

Agar lambda ichida bir nechta qator bo‘lsa, {} ishlatiladi.

3. Functional Interface

Functional interface — ichida faqat bitta abstract method bo‘lgan interface.

Masalan:

@FunctionalInterface
public interface Calculator {
    int calculate(int a, int b);
}

Bu interface lambda bilan ishlatiladi:

Calculator sum = (a, b) -> a + b;

int result = sum.calculate(10, 20);

System.out.println(result);

Natija:

30

3.1 @FunctionalInterface nima qiladi?

@FunctionalInterface
public interface Calculator {
    int calculate(int a, int b);
}

Bu annotation Java’ga aytadi:

Bu interface functional interface bo‘lishi kerak.

Agar ikkinchi abstract method qo‘shib yuborsangiz, compile error beradi.

@FunctionalInterface
public interface Calculator {
    int calculate(int a, int b);

    int minus(int a, int b); // xato
}

4. Tayyor functional interfacelar

Java’da tayyor functional interfacelar bor. Eng keraklilari:

4.1 Predicate

Predicate — shart tekshiradi. Natija true yoki false.

Predicate<Integer> isEven = number -> number % 2 == 0;

System.out.println(isEven.test(10));
System.out.println(isEven.test(7));

Natija:

true
false

Real misol:

List<Integer> numbers = List.of(1, 2, 3, 4, 5, 6);

List<Integer> evenNumbers = numbers.stream()
        .filter(number -> number % 2 == 0)
        .toList();

System.out.println(evenNumbers);

Natija:

[2, 4, 6]

4.2 Function

Function<T, R> — bitta qiymat olib, boshqa qiymat qaytaradi.

Function<String, Integer> lengthFunction = text -> text.length();

System.out.println(lengthFunction.apply("Java"));

Natija:

4

Real misol:

List<String> names = List.of("Ali", "Vali", "Hasan");

List<Integer> lengths = names.stream()
        .map(name -> name.length())
        .toList();

System.out.println(lengths);

Natija:

[3, 4, 5]

4.3 Consumer

Consumer<T> — qiymat oladi, lekin hech narsa qaytarmaydi.

Consumer<String> printer = text -> System.out.println(text);

printer.accept("Hello Java");

Real misol:

List<String> names = List.of("Ali", "Vali", "Hasan");

names.forEach(name -> System.out.println(name));

4.4 Supplier

Supplier<T> — parameter olmaydi, qiymat qaytaradi.

Supplier<Double> randomSupplier = () -> Math.random();

System.out.println(randomSupplier.get());

Real misol:

Supplier<LocalDateTime> nowSupplier = () -> LocalDateTime.now();

System.out.println(nowSupplier.get());

5. Stream API

Stream API — collection ichidagi ma’lumotlarni functional uslubda qayta ishlash uchun ishlatiladi.

Stream yordamida:

• filter qilish;

• map qilish;

• sort qilish;

• count qilish;

• group qilish;

• reduce qilish;

• listga yig‘ish;

mumkin.

5.1 Oddiy stream misol

List<String> names = List.of("Ali", "Vali", "Hasan", "Aziz");

List<String> result = names.stream()
        .filter(name -> name.startsWith("A"))
        .toList();

System.out.println(result);

Natija:

[Ali, Aziz]

Bu yerda:

names.stream()

collectionni streamga aylantiradi.

.filter(name -> name.startsWith("A"))

faqat A bilan boshlanadiganlarni qoldiradi.

.toList()

natijani listga yig‘adi.

6. Stream filter

filter — shartga mos elementlarni qoldiradi.

List<Integer> numbers = List.of(1, 2, 3, 4, 5, 6);

List<Integer> evenNumbers = numbers.stream()
        .filter(number -> number % 2 == 0)
        .toList();

System.out.println(evenNumbers);

Natija:

[2, 4, 6]

7. Stream map

map — har bir elementni boshqa ko‘rinishga o‘zgartiradi.

List<String> names = List.of("Ali", "Vali", "Hasan");

List<String> upperNames = names.stream()
        .map(name -> name.toUpperCase())
        .toList();

System.out.println(upperNames);

Natija:

[ALI, VALI, HASAN]

7.1 Entity’dan DTO yasash

Backend’da map juda ko‘p ishlatiladi.

public class User {
    private Long id;
    private String name;

    public User(Long id, String name) {
        this.id = id;
        this.name = name;
    }

    public Long getId() {
        return id;
    }

    public String getName() {
        return name;
    }
}

public class UserDto {
    private Long id;
    private String name;

    public UserDto(Long id, String name) {
        this.id = id;
        this.name = name;
    }
}

Listni DTO’ga o‘tkazish:

List<UserDto> userDtos = users.stream()
        .map(user -> new UserDto(user.getId(), user.getName()))
        .toList();

Bu real Spring Boot loyihalarda juda ko‘p ishlatiladi.

8. Stream sorted

List<Integer> numbers = List.of(5, 1, 4, 2, 3);

List<Integer> sortedNumbers = numbers.stream()
        .sorted()
        .toList();

System.out.println(sortedNumbers);

Natija:

[1, 2, 3, 4, 5]

Objectlarni sort qilish:

List<User> sortedUsers = users.stream()
        .sorted(Comparator.comparing(User::getName))
        .toList();

Age bo‘yicha kamayish tartibida:

List<User> sortedUsers = users.stream()
        .sorted(Comparator.comparing(User::getAge).reversed())
        .toList();

9. Stream forEach

forEach — har bir element ustida amal bajaradi.

List<String> names = List.of("Ali", "Vali", "Hasan");

names.stream()
        .forEach(name -> System.out.println(name));

Yoki:

names.forEach(name -> System.out.println(name));

Yanada qisqa:

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

Muhim: forEach odatda natija qaytarmaydi. Faqat amal bajaradi.

10. Stream count

List<String> names = List.of("Ali", "Vali", "Hasan", "Aziz");

long count = names.stream()
        .filter(name -> name.startsWith("A"))
        .count();

System.out.println(count);

Natija:

2

11. Stream findFirst

List<String> names = List.of("Ali", "Vali", "Hasan");

Optional<String> first = names.stream()
        .filter(name -> name.startsWith("A"))
        .findFirst();

System.out.println(first.orElse("Topilmadi"));

Natija:

Ali

findFirst() natijasi Optional bo‘ladi. Chunki element topilmasligi ham mumkin.

12. Stream anyMatch, allMatch, noneMatch

anyMatch

Kamida bittasi mos kelsa true.

boolean hasAdult = users.stream()
        .anyMatch(user -> user.getAge() >= 18);

allMatch

Hammasi mos kelsa true.

boolean allAdults = users.stream()
        .allMatch(user -> user.getAge() >= 18);

noneMatch

Hech biri mos kelmasa true.

boolean noBlockedUsers = users.stream()
        .noneMatch(user -> user.isBlocked());

13. Stream reduce

reduce — collection ichidagi qiymatlarni bitta natijaga yig‘adi.

Masalan, sonlar yig‘indisi:

List<Integer> numbers = List.of(1, 2, 3, 4);

int sum = numbers.stream()
        .reduce(0, (a, b) -> a + b);

System.out.println(sum);

Natija:

10

Qisqaroq:

int sum = numbers.stream()
        .reduce(0, Integer::sum);

14. Collectors

Collectors — stream natijasini yig‘ish uchun ishlatiladi.

Java 16+ da ko‘p joyda .toList() ishlatsa bo‘ladi:

List<String> result = names.stream()
        .filter(name -> name.startsWith("A"))
        .toList();

Lekin Java 8’da odatda bunday yoziladi:

List<String> result = names.stream()
        .filter(name -> name.startsWith("A"))
        .collect(Collectors.toList());

14.1 Setga yig‘ish

Set<String> uniqueNames = names.stream()
        .collect(Collectors.toSet());

14.2 Mapga yig‘ish

Map<Long, User> usersById = users.stream()
        .collect(Collectors.toMap(
                User::getId,
                user -> user
        ));

Bu real backend’da juda foydali.

Masalan, List<User> bor. Sizga id -> user ko‘rinishida Map kerak.

14.3 groupingBy

groupingBy — ma’lumotlarni guruhlash.

Masalan, userlarni age bo‘yicha guruhlash:

Map<Integer, List<User>> usersByAge = users.stream()
        .collect(Collectors.groupingBy(User::getAge));

Orderlarni status bo‘yicha guruhlash:

Map<OrderStatus, List<Order>> ordersByStatus = orders.stream()
        .collect(Collectors.groupingBy(Order::getStatus));

Natija taxminan:

NEW -> [order1, order2]
PAID -> [order3, order4]
CANCELLED -> [order5]

15. Stream API’da muhim tushuncha

Stream operationlar ikki turga bo‘linadi:

Intermediate operations

Bular streamni qayta ishlaydi, lekin darhol ishga tushmaydi:

• filter

• map

• sorted

• distinct

• limit

• skip

Terminal operations

Bular streamni ishga tushiradi:

• toList

• collect

• forEach

• count

• findFirst

• reduce

• anyMatch

Misol:

List<String> result = names.stream()
        .filter(name -> name.startsWith("A"))
        .map(String::toUpperCase)
        .toList();

Bu yerda:

filter -> intermediate
map -> intermediate
toList -> terminal

Terminal operation bo‘lmasa, stream ishlamaydi.

16. Method Reference

Method reference — lambda’ni yanada qisqa yozish usuli.

Lambda:

names.forEach(name -> System.out.println(name));

Method reference:

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

16.1 Method reference turlari

Static method reference

Function<String, Integer> parser = Integer::parseInt;

Bu shunga teng:

Function<String, Integer> parser = text -> Integer.parseInt(text);

Instance method reference

List<String> upperNames = names.stream()
        .map(String::toUpperCase)
        .toList();

Bu shunga teng:

.map(name -> name.toUpperCase())

Constructor reference

Supplier<ArrayList<String>> listSupplier = ArrayList::new;

Bu shunga teng:

Supplier<ArrayList<String>> listSupplier = () -> new ArrayList<>();

17. Optional

Optional — qiymat bor yoki yo‘qligini xavfsiz ifodalash uchun ishlatiladi.

U null o‘rnini to‘liq bosmaydi, lekin method natijasida “topilishi ham, topilmasligi ham mumkin” degan holatni aniq ko‘rsatadi.

17.1 Optional yaratish

Optional<String> name = Optional.of("Ali");

Bo‘sh Optional:

Optional<String> empty = Optional.empty();

Null bo‘lishi mumkin bo‘lgan qiymatdan:

String text = getName();

Optional<String> optionalText = Optional.ofNullable(text);

ofNullable null kelsa xato bermaydi, Optional.empty() qiladi.

17.2 Optional ishlatish

Yomon usul:

User user = userRepository.findById(1L);

if (user != null) {
    System.out.println(user.getName());
}

Yaxshi usul:

Optional<User> optionalUser = userRepository.findById(1L);

optionalUser.ifPresent(user -> System.out.println(user.getName()));

17.3 orElse

String name = optionalName.orElse("Noma'lum");

Agar qiymat bo‘lsa — o‘sha qiymat. Bo‘lmasa — "Noma'lum".

17.4 orElseThrow

Spring Boot’da juda ko‘p ishlatiladi:

User user = userRepository.findById(id)
        .orElseThrow(() -> new RuntimeException("User topilmadi"));

Bu degani:

User topilsa qaytar. Topilmasa exception ot.

17.5 Optional bilan map

Optional<String> userName = userRepository.findById(id)
        .map(User::getName);

Agar user topilsa, uning name’ini oladi. Topilmasa, empty qoladi.

17.6 Optional xatolari

Yomon:

Optional<User> user = userRepository.findById(id);

if (user.isPresent()) {
    System.out.println(user.get().getName());
}

Bu ishlaydi, lekin ko‘pincha chiroyli emas.

Yaxshiroq:

userRepository.findById(id)
        .ifPresent(user -> System.out.println(user.getName()));

Yoki kerak bo‘lsa:

User user = userRepository.findById(id)
        .orElseThrow(() -> new RuntimeException("User topilmadi"));

18. Default methods in interface

Java 8’dan boshlab interface ichida tayyor method yozish mumkin.

public interface PaymentService {
    void pay(double amount);

    default void printInfo() {
        System.out.println("Payment service");
    }
}

Implementation class printInfo()ni yozmasa ham bo‘ladi.

public class ClickPaymentService implements PaymentService {
    @Override
    public void pay(double amount) {
        System.out.println("Click orqali to'landi");
    }
}

Ishlatish:

PaymentService service = new ClickPaymentService();

service.pay(100_000);
service.printInfo();

18.1 Nega default method kerak?

Asosiy sabab:

Eski interface’ga yangi method qo‘shilganda, eski implementation classlar buzilib ketmasin.

Masalan, sizda interface bor:

public interface ReportService {
    void generate();
}

Keyin unga yangi method qo‘shmoqchisiz:

public interface ReportService {
    void generate();

    default void exportPdf() {
        System.out.println("PDF export qilindi");
    }
}

Endi eski classlar exportPdf()ni majburiy override qilishi shart emas.

19. Static methods in interface

Interface ichida static method ham yozish mumkin.

public interface MathUtils {
    static int square(int number) {
        return number * number;
    }
}

Ishlatish:

int result = MathUtils.square(5);

System.out.println(result);

Natija:

25

Static interface method obyekt orqali emas, interface nomi orqali chaqiriladi.

20. Date/Time API — java.time

Java 8’dan oldin Date va Calendar ishlatilardi. Ular noqulay va xatoga moyil edi.

Java 8’da yangi java.time API keldi.

Eng kerakli classlar:

20.1 LocalDate

LocalDate today = LocalDate.now();

System.out.println(today);

Natija:

2026-05-20

Sana yaratish:

LocalDate birthDate = LocalDate.of(2000, 5, 10);

20.2 LocalTime

LocalTime now = LocalTime.now();

System.out.println(now);

20.3 LocalDateTime

LocalDateTime now = LocalDateTime.now();

System.out.println(now);

Bu sana va vaqtni beradi, lekin timezone saqlamaydi.

20.4 Sana qo‘shish/ayirish

LocalDate today = LocalDate.now();

LocalDate tomorrow = today.plusDays(1);
LocalDate nextMonth = today.plusMonths(1);
LocalDate yesterday = today.minusDays(1);

20.5 DateTimeFormatter

LocalDate date = LocalDate.now();

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd.MM.yyyy");

String formatted = date.format(formatter);

System.out.println(formatted);

Natija:

20.05.2026

Stringdan date yasash:

String text = "20.05.2026";

LocalDate date = LocalDate.parse(
        text,
        DateTimeFormatter.ofPattern("dd.MM.yyyy")
);

21. Real backend misol: Order filter

Tasavvur qiling, orderlar ro‘yxati bor.

public class Order {
    private Long id;
    private String customerName;
    private OrderStatus status;
    private int amount;
    private LocalDateTime createdAt;

    public Order(Long id, String customerName, OrderStatus status, int amount, LocalDateTime createdAt) {
        this.id = id;
        this.customerName = customerName;
        this.status = status;
        this.amount = amount;
        this.createdAt = createdAt;
    }

    public Long getId() {
        return id;
    }

    public String getCustomerName() {
        return customerName;
    }

    public OrderStatus getStatus() {
        return status;
    }

    public int getAmount() {
        return amount;
    }

    public LocalDateTime getCreatedAt() {
        return createdAt;
    }
}

Status enum:

public enum OrderStatus {
    NEW,
    PAID,
    CANCELLED
}

Orderlarni filter qilish:

List<Order> paidOrders = orders.stream()
        .filter(order -> order.getStatus() == OrderStatus.PAID)
        .toList();

Summani hisoblash:

int totalAmount = orders.stream()
        .filter(order -> order.getStatus() == OrderStatus.PAID)
        .mapToInt(Order::getAmount)
        .sum();

Eng oxirgi orderni topish:

Optional<Order> latestOrder = orders.stream()
        .max(Comparator.comparing(Order::getCreatedAt));

Status bo‘yicha guruhlash:

Map<OrderStatus, List<Order>> ordersByStatus = orders.stream()
        .collect(Collectors.groupingBy(Order::getStatus));

22. Stream API’da ehtiyot bo‘lish kerak bo‘lgan joylar

22.1 Juda murakkab stream yozish

Yomon:

List<String> result = users.stream()
        .filter(u -> u.getAge() > 18)
        .filter(u -> !u.isBlocked())
        .map(u -> u.getOrders())
        .flatMap(o -> o.stream())
        .filter(o -> o.getAmount() > 100000)
        .map(o -> o.getProduct().getName())
        .distinct()
        .sorted()
        .toList();

Bu ishlaydi, lekin o‘qish qiyin.

Bunday holatda oddiy methodlarga ajratgan yaxshi.

22.2 Stream ichida side effect qilish

Yomon:

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

users.stream()
        .filter(user -> user.getAge() > 18)
        .forEach(user -> result.add(user.getName()));

Yaxshi:

List<String> result = users.stream()
        .filter(user -> user.getAge() > 18)
        .map(User::getName)
        .toList();

22.3 Null qiymatlar

Agar list ichida null bo‘lsa:

List<String> names = Arrays.asList("Ali", null, "Vali");

List<String> upperNames = names.stream()
        .map(String::toUpperCase)
        .toList();

Bu NullPointerException beradi.

Yaxshi:

List<String> upperNames = names.stream()
        .filter(Objects::nonNull)
        .map(String::toUpperCase)
        .toList();

23. Java 8+ features qayerda ko‘p ishlatiladi?

Spring Boot backend’da:

userRepository.findById(id)
        .orElseThrow(() -> new RuntimeException("User topilmadi"));

List<UserDto> users = userRepository.findAll().stream()
        .map(userMapper::toDto)
        .toList();

Map<Long, Product> productsById = products.stream()
        .collect(Collectors.toMap(Product::getId, product -> product));

orders.stream()
        .filter(order -> order.getStatus() == OrderStatus.PAID)
        .mapToInt(Order::getAmount)
        .sum();

24. Junior uchun eng muhim qismlar

25. Amaliy mashq

Vazifa: User filter system

User class yarating:

public class User {
    private Long id;
    private String name;
    private int age;
    private boolean active;

    public User(Long id, String name, int age, boolean active) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.active = active;
    }

    public Long getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    public boolean isActive() {
        return active;
    }
}

List yarating:

List<User> users = List.of(
        new User(1L, "Ali", 25, true),
        new User(2L, "Vali", 17, true),
        new User(3L, "Hasan", 30, false),
        new User(4L, "Aziz", 22, true)
);

Quyidagilarni bajaring:

1. Faqat active userlarni oling.

2. Faqat 18 yoshdan kattalarni oling.

3. User name’larini List<String> qilib oling.

4. Userlarni age bo‘yicha sort qiling.

5. Map<Long, User> yasang.

6. Active userlar sonini hisoblang.

7. Eng katta yoshli userni toping.

8. Optional<User> orqali id = 10 bo‘lgan userni qidiring.

9. Topilmasa "User topilmadi" exception chiqaring.

10. Bugungi sanani dd.MM.yyyy formatda chiqaring.

Xulosa

Java 8+ features Junior Java developer uchun juda muhim.

Asosiy eslab qoling:

list.stream()
        .filter(...)
        .map(...)
        .toList();

Optional<User> user = repository.findById(id);

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

LocalDate.now();
LocalDateTime.now();

Java 8+ sizga kodni:

• qisqaroq;

• o‘qilishi osonroq;

• xavfsizroq;

• functional uslubga yaqinroq;

• backend API uchun qulayroq

qilib yozishga yordam beradi.