Java asoslari 7-qism. Java Collections Framework

Java Collections Framework - Java’da obyektlar to‘plami bilan ishlash uchun tayyor kutubxona.

Oddiy qilib aytganda, bu:

• ro‘yxat saqlash;

• takrorlanmas qiymatlar saqlash;

• kalit-qiymat ko‘rinishida data saqlash;

• navbat bilan ishlash;

• saralash;

• qidirish;

• aylanish;

uchun kerak bo‘ladigan tayyor class va interfacelar to‘plami.

Bu mavzu alohida bo‘lim sifatida berilgan: List, Set, Map, Queue, ArrayList vs LinkedList, HashSet, TreeSet, HashMap, TreeMap, Collections, Comparable, Comparator.

1. Nega Collections kerak?

Masalan, sizda foydalanuvchilar ro‘yxati bor:

String user1 = "Ali";
String user2 = "Vali";
String user3 = "Hasan";

Bu yomon usul. Chunki foydalanuvchilar soni 3 ta emas, 3000 ta bo‘lishi mumkin.

Array ishlatsak:

String[] users = new String[3];

users[0] = "Ali";
users[1] = "Vali";
users[2] = "Hasan";

Lekin array’da muammo bor:

• hajmi oldindan beriladi;

• element qo‘shish/noqulay;

• o‘chirish/noqulay;

• qidirish uchun tayyor imkoniyat kam;

• real loyihalarda moslashuvchan emas.

Shuning uchun Java’da Collections Framework ishlatiladi.

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

users.add("Ali");
users.add("Vali");
users.add("Hasan");

Bu ancha qulay.

2. Collection hierarchy oddiy ko‘rinishda

Java Collections ichida asosiy turlar:

Collection
 ├── List
 ├── Set
 └── Queue

Map

E’tibor bering: Map Collection ichiga kirmaydi, lekin Collections Framework’ning muhim qismi hisoblanadi.

3. List

List - tartibli ro‘yxat.

Asosiy xususiyatlari:

• elementlar tartib bilan saqlanadi;

• duplicate qiymatga ruxsat beradi;

• index orqali murojaat qilish mumkin;

• 0 dan boshlanadi.

Misol:

import java.util.ArrayList;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<String> names = new ArrayList<>();

        names.add("Ali");
        names.add("Vali");
        names.add("Ali");

        System.out.println(names);
    }
}

Natija:

[Ali, Vali, Ali]

Bu yerda "Ali" ikki marta bor. List bunga ruxsat beradi.

3.1 List ichidan element olish

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

names.add("Ali");
names.add("Vali");
names.add("Hasan");

String firstName = names.get(0);

System.out.println(firstName);

Natija:

Ali

3.2 List ichidagi elementni o‘zgartirish

names.set(1, "Sardor");

Oldin:

[Ali, Vali, Hasan]

Keyin:

[Ali, Sardor, Hasan]

3.3 List ichidan element o‘chirish

names.remove("Ali");

Yoki index orqali:

names.remove(0);

Ehtiyot bo‘lish kerak:

List<Integer> numbers = new ArrayList<>();

numbers.add(10);
numbers.add(20);
numbers.add(30);

numbers.remove(1);

Bu yerda 1 qiymatini emas, 1-indexdagi elementni o‘chiradi. Ya’ni 20 o‘chadi.

Agar qiymat bo‘yicha o‘chirmoqchi bo‘lsak:

numbers.remove(Integer.valueOf(10));

4. ArrayList

ArrayList - List interface’ining eng ko‘p ishlatiladigan implementation’i.

Ichkarida array ishlatadi.

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

ArrayList kuchli tomonlari:

• index orqali tez o‘qiydi;

• oddiy ro‘yxatlar uchun eng yaxshi default tanlov;

• ko‘p holatda List kerak bo‘lsa, ArrayList ishlatiladi.

Kamchiliklari:

• o‘rtasidan element qo‘shish yoki o‘chirish sekinroq;

• ichki array to‘lsa, yangi kattaroq array yaratadi va eski elementlarni ko‘chiradi.

5. LinkedList

LinkedList - elementlarni zanjir shaklida saqlaydi.

Har bir element keyingi va oldingi elementga link saqlaydi.

List<String> names = new LinkedList<>();

LinkedList kuchli tomoni:

• boshidan yoki o‘rtasidan qo‘shish/o‘chirish ayrim holatlarda qulay.

Kamchiliklari:

• index orqali o‘qish sekin;

• ko‘proq xotira ishlatadi;

• real backend loyihalarda ArrayListga qaraganda kamroq ishlatiladi.

5.1 ArrayList vs LinkedList

Junior uchun qoida:

Default holatda ArrayList ishlating. LinkedListni faqat aniq sabab bo‘lsa ishlating.

6. Set

Set - takrorlanmas qiymatlar to‘plami.

Asosiy xususiyatlari:

• duplicate qiymat saqlamaydi;

• index yo‘q;

• tartib har doim kafolatlanmaydi.

Misol:

import java.util.HashSet;
import java.util.Set;

public class Main {
    public static void main(String[] args) {
        Set<String> names = new HashSet<>();

        names.add("Ali");
        names.add("Vali");
        names.add("Ali");

        System.out.println(names);
    }
}

Natija taxminan:

[Vali, Ali]

Ali ikki marta qo‘shildi, lekin faqat bittasi saqlandi.

7. HashSet

HashSet - Setning eng ko‘p ishlatiladigan implementation’i.

Kuchli tomoni:

• tez qo‘shadi;

• tez qidiradi;

• duplicate qiymatlarni avtomatik olib tashlaydi.

Misol:

Set<Integer> ids = new HashSet<>();

ids.add(101);
ids.add(102);
ids.add(101);

System.out.println(ids);

Natija:

[101, 102]

Tartib kafolatlanmaydi.

8. LinkedHashSet

LinkedHashSet - duplicate qiymat saqlamaydi, lekin qo‘shilgan tartibni saqlaydi.

Set<String> names = new LinkedHashSet<>();

names.add("Ali");
names.add("Vali");
names.add("Hasan");

System.out.println(names);

Natija:

[Ali, Vali, Hasan]

Qachon kerak?

Masalan, siz duplicate’larni olib tashlamoqchisiz, lekin eski tartib saqlanib qolsin.

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

Set<String> uniqueNames = new LinkedHashSet<>(list);

System.out.println(uniqueNames);

Natija:

[Ali, Vali, Hasan]

9. TreeSet

TreeSet - elementlarni saralangan holda saqlaydi.

Set<Integer> numbers = new TreeSet<>();

numbers.add(30);
numbers.add(10);
numbers.add(20);

System.out.println(numbers);

Natija:

[10, 20, 30]

String bilan:

Set<String> names = new TreeSet<>();

names.add("Vali");
names.add("Ali");
names.add("Hasan");

System.out.println(names);

Natija:

[Ali, Hasan, Vali]

TreeSet tartiblab beradi, lekin HashSetga qaraganda sekinroq bo‘lishi mumkin.

10. Map

Map - kalit va qiymat saqlaydi.

key -> value

Masalan:

username -> password
userId   -> user
phone    -> customer

Misol:

import java.util.HashMap;
import java.util.Map;

public class Main {
    public static void main(String[] args) {
        Map<Integer, String> users = new HashMap<>();

        users.put(1, "Ali");
        users.put(2, "Vali");
        users.put(3, "Hasan");

        System.out.println(users.get(1));
    }
}

Natija:

Ali

10.1 Map’da key unique bo‘ladi

Map<Integer, String> users = new HashMap<>();

users.put(1, "Ali");
users.put(1, "Vali");

System.out.println(users);

Natija:

{1=Vali}

Bitta key ikki marta qo‘yildi. Eski qiymat yangisiga almashtirildi.

11. HashMap

HashMap - Mapning eng ko‘p ishlatiladigan implementation’i.

Kuchli tomoni:

• key orqali tez topadi;

• ko‘p real loyihalarda default tanlov;

• cache, lookup, mapping uchun qulay.

Misol:

Map<String, Integer> productPrices = new HashMap<>();

productPrices.put("apple", 10_000);
productPrices.put("banana", 15_000);

Integer applePrice = productPrices.get("apple");

System.out.println(applePrice);

Natija:

10000

11.1 containsKey

if (productPrices.containsKey("apple")) {
    System.out.println("Apple mavjud");
}

Bu key bor-yo‘qligini tekshiradi.

11.2 getOrDefault

int price = productPrices.getOrDefault("orange", 0);

System.out.println(price);

Agar "orange" key bo‘lmasa, 0 qaytaradi.

11.3 putIfAbsent

productPrices.putIfAbsent("apple", 20_000);

Agar "apple" oldindan mavjud bo‘lsa, qiymatni almashtirmaydi.

12. LinkedHashMap

LinkedHashMap - HashMapga o‘xshaydi, lekin qo‘shilgan tartibni saqlaydi.

Map<Integer, String> users = new LinkedHashMap<>();

users.put(3, "Hasan");
users.put(1, "Ali");
users.put(2, "Vali");

System.out.println(users);

Natija:

{3=Hasan, 1=Ali, 2=Vali}

Qo‘shilgan tartib saqlanadi.

13. TreeMap

TreeMap - key bo‘yicha saralab saqlaydi.

Map<Integer, String> users = new TreeMap<>();

users.put(3, "Hasan");
users.put(1, "Ali");
users.put(2, "Vali");

System.out.println(users);

Natija:

{1=Ali, 2=Vali, 3=Hasan}

Qachon ishlatiladi?

• keylar tartibli bo‘lishi kerak bo‘lsa;

• range query kerak bo‘lsa;

• eng kichik/eng katta key bilan ishlash kerak bo‘lsa.

14. Queue

Queue - navbat.

Birinchi kirgan birinchi chiqadi.

Ali -> Vali -> Hasan

Bu FIFO deyiladi:

First In, First Out

Misol:

Queue<String> queue = new LinkedList<>();

queue.add("Ali");
queue.add("Vali");
queue.add("Hasan");

System.out.println(queue.poll());
System.out.println(queue.poll());

Natija:

Ali
Vali

14.1 Queue methodlari

Misol:

Queue<String> queue = new LinkedList<>();

queue.offer("Ali");
queue.offer("Vali");

System.out.println(queue.peek());
System.out.println(queue.poll());
System.out.println(queue.poll());

Natija:

Ali
Ali
Vali

15. ArrayDeque

Queue uchun ko‘p holatda ArrayDeque yaxshi tanlov.

Queue<String> queue = new ArrayDeque<>();

queue.offer("Ali");
queue.offer("Vali");

System.out.println(queue.poll());

Junior uchun qoida:

Oddiy queue kerak bo‘lsa, ArrayDeque ishlating.
Faqat List ham kerak bo‘lsa, LinkedList ishlatish mumkin.

16. Collections utility class

Collections - collectionlar bilan ishlash uchun yordamchi class.

16.1 Sort qilish

List<Integer> numbers = new ArrayList<>();

numbers.add(30);
numbers.add(10);
numbers.add(20);

Collections.sort(numbers);

System.out.println(numbers);

Natija:

[10, 20, 30]

16.2 Reverse qilish

Collections.reverse(numbers);

Natija:

[30, 20, 10]

16.3 Min va max

int min = Collections.min(numbers);
int max = Collections.max(numbers);

17. Comparable

Comparable - obyekt o‘zini qanday sort qilishni biladi.

Masalan, Userni age bo‘yicha sort qilamiz.

public class User implements Comparable<User> {
    private String name;
    private int age;

    public User(String name, int age) {
        this.name = name;
        this.age = age;
    }

    @Override
    public int compareTo(User other) {
        return Integer.compare(this.age, other.age);
    }

    @Override
    public String toString() {
        return name + " - " + age;
    }
}

Ishlatish:

List<User> users = new ArrayList<>();

users.add(new User("Ali", 25));
users.add(new User("Vali", 20));
users.add(new User("Hasan", 30));

Collections.sort(users);

System.out.println(users);

Natija:

[Vali - 20, Ali - 25, Hasan - 30]

Bu yerda sort age bo‘yicha bo‘ldi.

18. Comparator

Comparator - tashqaridan sort qilish qoidasi beriladi.

Masalan, name bo‘yicha sort:

users.sort((u1, u2) -> u1.getName().compareTo(u2.getName()));

Buning uchun getName() kerak:

public String getName() {
    return name;
}

Yaxshiroq ko‘rinish:

users.sort(Comparator.comparing(User::getName));

Age bo‘yicha:

users.sort(Comparator.comparing(User::getAge));

Teskarisiga sort qilish:

users.sort(Comparator.comparing(User::getAge).reversed());

19. Comparable vs Comparator

Misol:

• User doim age bo‘yicha sort qilinsin desak - Comparable;

• ba’zida name, ba’zida age, ba’zida createdDate bo‘yicha sort kerak bo‘lsa - Comparator.

Real loyihalarda Comparator ko‘proq moslashuvchan.

20. Real backend misol

Tasavvur qiling, productlar ro‘yxati bor.

public class Product {
    private Long id;
    private String name;
    private int price;

    public Product(Long id, String name, int price) {
        this.id = id;
        this.name = name;
        this.price = price;
    }

    public Long getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public int getPrice() {
        return price;
    }
}

Productlarni id bo‘yicha tez topish kerak bo‘lsa:

Map<Long, Product> productMap = new HashMap<>();

Product product = new Product(1L, "Laptop", 500);

productMap.put(product.getId(), product);

Product found = productMap.get(1L);

Bu real backend’da juda ko‘p uchraydi.

Masalan:

Map<Long, User> usersById;
Map<String, User> usersByPhone;
Map<String, Product> productsByCode;
Set<Long> blockedUserIds;
List<Order> orders;

21. Qaysi collectionni qachon ishlatamiz?

22. Eng ko‘p ishlatiladiganlari

Junior backend uchun eng keraklilari:

List
ArrayList
Set
HashSet
Map
HashMap
Comparator
Collections

Keyinroq:

LinkedHashMap
TreeMap
Queue
ArrayDeque
TreeSet

Kamroq:

LinkedList
Vector
Stack
Hashtable

Vector, Stack, Hashtable eski classlar. Yangi kodda kam ishlatiladi.

23. Juniorlar qiladigan xatolar

Xato 1: ArrayList o‘rniga hamma joyda LinkedList ishlatish

Ko‘p holatda ArrayList yaxshiroq.

Xato 2: HashMap.get() null qaytarishini unutish

User user = users.get(10L);
user.getName();

Agar user topilmasa, NullPointerException bo‘ladi.

Yaxshiroq:

User user = users.get(10L);

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

Xato 3: Set tartibini kutish

Set<String> names = new HashSet<>();

HashSet tartibni kafolatlamaydi.

Tartib kerak bo‘lsa:

Set<String> names = new LinkedHashSet<>();

Xato 4: Objectlarda equals() va hashCode() yozmaslik

Masalan:

Set<User> users = new HashSet<>();

Agar User classida equals() va hashCode() noto‘g‘ri bo‘lsa, duplicate muammosi chiqadi.

Bu alohida muhim mavzu.

24. Kichik amaliy mashq

Vazifa: Student Management

Student class yarating:

public class Student {
    private Long id;
    private String name;
    private int age;
    private int score;
}

Quyidagilarni bajaring:

1. List<Student> yarating.

2. 5 ta student qo‘shing.

3. Studentlarni score bo‘yicha kamayish tartibida sort qiling.

4. Studentlarni age bo‘yicha o‘sish tartibida sort qiling.

5. Map<Long, Student> yarating.

6. Studentlarni id bo‘yicha mapga joylang.

7. Bitta studentni id orqali toping.

8. Duplicate name’larni Set<String> orqali olib tashlang.

25. Xulosa

Java Collections Framework - Java developer uchun eng muhim mavzulardan biri.

Asosiy eslab qolish kerak:

• List - tartibli ro‘yxat;

• Set - duplicate yo‘q;

• Map - key-value;

• Queue - navbat;

• ArrayList - default ro‘yxat tanlovi;

• HashSet - unique qiymatlar uchun;

• HashMap - key orqali tez topish uchun;

• Comparator - sort qilish uchun.