Java asoslari 5-qism

6. Error Handling Basics

Error handling - dasturda xatolik bo‘lganda uni nazorat qilish mexanizmi.

Real dasturda xato doim bo‘ladi:

• Fayl topilmaydi

• Internet uziladi

• Database ishlamay qoladi

• User noto‘g‘ri input beradi

• Null qiymat keladi

• Raqam o‘rniga matn kiritiladi

Java’da bunday holatlar Exception orqali boshqariladi.

Roadmapdagi Beginner bo‘limida bu qism quyidagilarni o‘z ichiga oladi: exceptions hierarchy,try/catch/finally, checked vs unchecked exceptions, throw & throws.

6.1. Exception nima?

Exception - dastur ishlayotgan paytda yuz beradigan xatolik.

Masalan:

int result = 10 / 0;
System.out.println(result);

Bu kod xato beradi:

ArithmeticException: / by zero

Chunki sonni 0 ga bo‘lib bo‘lmaydi.

Yana misol:

String name = null;
System.out.println(name.length());

Bu xato beradi:

NullPointerException

Chunki null object emas. Unda length() methodi yo‘q.

6.2. Compile-time error va runtime error

Java’da xatolarni ikki katta turga ajratish mumkin.

Compile-time error

Kod compile bo‘lmaydi.

int age = "Ali";

Bu xato. Chunki int ichiga String berilyapti.

Compiler bu kodni ishga tushirishga ham ruxsat bermaydi.

Runtime error

Kod compile bo‘ladi, lekin ishlayotgan paytda yiqiladi.

int a = 10;
int b = 0;

System.out.println(a / b);

Bu compile bo‘ladi. Lekin ishlaganda xato beradi:

ArithmeticException

Exception asosan runtime paytdagi xatolar bilan bog‘liq.

6.3. Exception hierarchy

Java’da exception’lar class ko‘rinishida qurilgan.

Soddalashtirilgan ko‘rinish:

Throwable
├── Error
└── Exception
    ├── Checked Exception
    └── RuntimeException
        └── Unchecked Exception

Muhim qismlar:

6.4. Error va Exception farqi

Error

Error odatda jiddiy system/JVM muammosi.

Masalan:

OutOfMemoryError
StackOverflowError

Bularni odatda try/catch bilan ushlab, davom etish yaxshi amaliyot emas.

Masalan:

public class Main {
    public static void main(String[] args) {
        main(args);
    }
}

Bu cheksiz recursion qiladi va oxirida:

StackOverflowError

chiqadi.

Exception

Exception - dasturda yuz berishi mumkin bo‘lgan xato.

Masalan:

FileNotFoundException
IOException
SQLException
NumberFormatException
NullPointerException

Bularni ayrim holatda ushlash, log qilish, userga tushunarli xabar berish kerak.

6.5. try / catch

Agar xato chiqishi mumkin bo‘lgan kod bo‘lsa, uni try ichiga yozamiz.

try {
    int result = 10 / 0;
    System.out.println(result);
} catch (ArithmeticException e) {
    System.out.println("Nolga bo‘lish mumkin emas");
}

Natija:

Nolga bo‘lish mumkin emas

Tushunish:

try   → xato chiqishi mumkin bo‘lgan kod
catch → xato chiqsa bajariladigan kod

6.6. try/catch qanday ishlaydi?

try {
    System.out.println("1");
    int result = 10 / 0;
    System.out.println("2");
} catch (ArithmeticException e) {
    System.out.println("Xato ushlandi");
}

System.out.println("3");

Natija:

1
Xato ushlandi
3

Nega 2 chiqmadi?

Chunki exception chiqqan joydan boshlab try ichidagi qolgan kod bajarilmaydi. Java darhol mos catch blokka o‘tadi.

6.7. Exception object

catch ichidagi e - exception object.

try {
    int result = 10 / 0;
} catch (ArithmeticException e) {
    System.out.println(e.getMessage());
}

Natija:

/ by zero

Ko‘p ishlatiladigan methodlar:

e.getMessage();      // xato xabari
e.printStackTrace(); // xato qayerda chiqqanini chiqaradi

Misol:

try {
    int result = 10 / 0;
} catch (ArithmeticException e) {
    e.printStackTrace();
}

printStackTrace() debug uchun foydali, lekin production’da odatda logging framework bilan log qilinadi.

6.8. Bir nechta catch

Bitta try uchun bir nechta catch yozish mumkin.

try {
    String text = null;
    System.out.println(text.length());
} catch (NullPointerException e) {
    System.out.println("Null qiymat bilan ishlash mumkin emas");
} catch (Exception e) {
    System.out.println("Boshqa xato yuz berdi");
}

Bu yerda NullPointerException chiqsa, birinchi catch ishlaydi.

Muhim qoida:

Specific exception yuqorida,
general exception pastda turishi kerak.

Noto‘g‘ri:

try {
    String text = null;
    System.out.println(text.length());
} catch (Exception e) {
    System.out.println("Boshqa xato");
} catch (NullPointerException e) {
    System.out.println("Null xato");
}

Bu compile error beradi. Chunki Exception hamma exceptionlarni ushlab qo‘yadi. Pastdagi NullPointerExceptionga navbat yetmaydi.

To‘g‘ri:

try {
    String text = null;
    System.out.println(text.length());
} catch (NullPointerException e) {
    System.out.println("Null xato");
} catch (Exception e) {
    System.out.println("Boshqa xato");
}

6.9. Multi-catch

Agar bir nechta exception uchun bir xil kod yozilsa:

try {
    String text = "abc";
    int number = Integer.parseInt(text);
    System.out.println(number);
} catch (NumberFormatException | NullPointerException e) {
    System.out.println("Input noto‘g‘ri");
}

Bu yerda NumberFormatException yoki NullPointerException chiqsa, bitta catch ishlaydi.

6.10. finally

finally - exception bo‘ladimi yo‘qmi, baribir bajariladigan blok.

try {
    int result = 10 / 2;
    System.out.println(result);
} catch (ArithmeticException e) {
    System.out.println("Xato");
} finally {
    System.out.println("Finally ishladi");
}

Natija:

5
Finally ishladi

Agar exception chiqsa ham:

try {
    int result = 10 / 0;
    System.out.println(result);
} catch (ArithmeticException e) {
    System.out.println("Xato");
} finally {
    System.out.println("Finally ishladi");
}

Natija:

Xato
Finally ishladi

6.11. finally nima uchun kerak?

finally odatda resurslarni yopish uchun ishlatiladi:

Faylni yopish
Database connection yopish
Network connection yopish
Lock bo‘shatish

Masalan soddalashtirilgan misol:

try {
    System.out.println("Fayl o‘qilyapti");
} catch (Exception e) {
    System.out.println("Xato yuz berdi");
} finally {
    System.out.println("Fayl yopildi");
}

Hozirgi Java’da resurslar uchun ko‘proq try-with-resources ishlatiladi. Lekin beginner bosqichida finally tushunchasini bilish kerak.

6.12. Checked va unchecked exception

Java’da exception ikki katta turga bo‘linadi:

Checked exception
Unchecked exception

Checked exception

Checked exception - compiler majburiy tekshirtiradigan exception.

Masalan:

import java.io.FileReader;

public class Main {
    public static void main(String[] args) {
        FileReader reader = new FileReader("data.txt");
    }
}

Bu compile bo‘lmaydi. Chunki FileReader FileNotFoundException chiqarishi mumkin.

Java aytadi:

Bu xatoni try/catch qil yoki throws bilan e’lon qil.

To‘g‘ri variant:

import java.io.FileReader;
import java.io.FileNotFoundException;

public class Main {
    public static void main(String[] args) {
        try {
            FileReader reader = new FileReader("data.txt");
        } catch (FileNotFoundException e) {
            System.out.println("Fayl topilmadi");
        }
    }
}

Checked exception misollari:

IOException
FileNotFoundException
SQLException
ClassNotFoundException

Unchecked exception

Unchecked exception - compiler majburlamaydigan exception.

Masalan:

int result = 10 / 0;

Compiler buni compile qiladi. Lekin runtime’da:

ArithmeticException

chiqadi.

Unchecked exceptionlar odatda RuntimeExceptiondan meros oladi.

Misollar:

NullPointerException
ArithmeticException
ArrayIndexOutOfBoundsException
NumberFormatException
IllegalArgumentException

6.13. Checked vs unchecked farqi

Oddiy tushuncha:

Checked    → Java oldindan: "bu xato bo‘lishi mumkin, hal qil" deydi
Unchecked  → Java majburlamaydi, lekin runtime’da yiqilishi mumkin

6.14. throw

throw - o‘zimiz exception chiqarish uchun ishlatiladi.

Masalan, yosh manfiy bo‘lmasligi kerak:

public class User {
    private int age;

    public void setAge(int age) {
        if (age < 0) {
            throw new IllegalArgumentException("Age manfiy bo‘lishi mumkin emas");
        }

        this.age = age;
    }
}

Ishlatish:

User user = new User();
user.setAge(-5);

Natija:

IllegalArgumentException: Age manfiy bo‘lishi mumkin emas

Bu yaxshi, chunki noto‘g‘ri qiymat object ichiga kirib ketmaydi.

6.15. throw qachon ishlatiladi?

throw quyidagi holatlarda foydali:

Noto‘g‘ri argument kelganda
Business rule buzilganda
Kerakli ma’lumot topilmaganda
Dastur davom etishi xavfli bo‘lganda

Masalan:

public void withdraw(double amount) {
    if (amount <= 0) {
        throw new IllegalArgumentException("Amount musbat bo‘lishi kerak");
    }

    System.out.println("Pul yechildi: " + amount);
}

6.16. throws

throws - method exception chiqarishi mumkinligini e’lon qiladi.

Masalan checked exception bilan:

import java.io.FileReader;
import java.io.FileNotFoundException;

public class Main {
    public static void main(String[] args) throws FileNotFoundException {
        FileReader reader = new FileReader("data.txt");
    }
}

Bu yerda:

throws FileNotFoundException

degani:

Bu method FileNotFoundException chiqarishi mumkin.
Uni chaqirgan joy hal qilsin.

6.17. throw va throws farqi

Misol:

public void checkAge(int age) {
    if (age < 18) {
        throw new IllegalArgumentException("Yosh yetmaydi");
    }
}

Bu yerda throw ishlatildi.

public void readFile() throws IOException {
    // file o‘qish
}

Bu yerda throws ishlatildi.

Qisqa:

throw  → action
throws → declaration

6.18. Custom exception

O‘zimizning exception class yaratishimiz mumkin.

Masalan:

public class NotEnoughBalanceException extends RuntimeException {
    public NotEnoughBalanceException(String message) {
        super(message);
    }
}

Ishlatish:

public class BankAccount {
    private double balance;

    public BankAccount(double balance) {
        this.balance = balance;
    }

    public void withdraw(double amount) {
        if (amount > balance) {
            throw new NotEnoughBalanceException("Balans yetarli emas");
        }

        balance -= amount;
    }
}

Main:

public class Main {
    public static void main(String[] args) {
        BankAccount account = new BankAccount(100);

        account.withdraw(150);
    }
}

Natija:

NotEnoughBalanceException: Balans yetarli emas

Bu real loyihalarda juda foydali. Chunki exception nomidan ham xato turi tushunarli bo‘ladi.

6.19. Exceptionni yutib yubormaslik

Yomon amaliyot:

try {
    int result = 10 / 0;
} catch (Exception e) {
}

Bu juda yomon. Chunki xato bo‘ldi, lekin hech narsa qilinmadi.

Kamida log yoki xabar bo‘lishi kerak:

try {
    int result = 10 / 0;
} catch (Exception e) {
    System.out.println("Xato: " + e.getMessage());
}

Real projectlarda:

log.error("Failed to calculate result", e);

ko‘rinishida log qilinadi.

6.20. Har joyda try/catch yozish ham yomon

Yana bir yomon amaliyot:

try {
    try {
        try {
            // code
        } catch (Exception e) {
        }
    } catch (Exception e) {
    }
} catch (Exception e) {
}

Kod juda chalkash bo‘ladi.

Yaxshi yondashuv:

Exceptionni kerakli darajada ushla
Pastki methodda faqat ma’no bo‘lsa ushla
Aks holda yuqoriga throw qil
Controller/global handler darajasida userga javob qaytar

Spring Boot’da odatda @ControllerAdvice orqali global exception handling qilinadi. Bu keyingi bosqichlarda chuqur o‘rganiladi.

6.21. NullPointerException

Java’da eng ko‘p uchraydigan exceptionlardan biri.

String name = null;
System.out.println(name.length());

Xato:

NullPointerException

Sabab:

name null, ya’ni object yo‘q.
Object yo‘q bo‘lsa, method chaqirib bo‘lmaydi.

Oldini olish:

String name = null;

if (name != null) {
    System.out.println(name.length());
}

Yoki String solishtirishda xavfsizroq usul:

String role = null;

if ("ADMIN".equals(role)) {
    System.out.println("Admin user");
}

Bu xato bermaydi.

Lekin bu xato berishi mumkin:

if (role.equals("ADMIN")) {
    System.out.println("Admin user");
}

Chunki role null bo‘lishi mumkin.

6.22. NumberFormatException

Matndan son yasashda xato bo‘lishi mumkin.

String text = "123";
int number = Integer.parseInt(text);

System.out.println(number);

Natija:

123

Lekin:

String text = "abc";
int number = Integer.parseInt(text);

Xato:

NumberFormatException

To‘g‘ri ishlov berish:

String text = "abc";

try {
    int number = Integer.parseInt(text);
    System.out.println(number);
} catch (NumberFormatException e) {
    System.out.println("Raqam noto‘g‘ri formatda");
}

6.23. ArrayIndexOutOfBoundsException

Array chegarasidan chiqilganda:

int[] numbers = {10, 20, 30};

System.out.println(numbers[3]);

Xato:

ArrayIndexOutOfBoundsException

To‘g‘ri:

int[] numbers = {10, 20, 30};

for (int i = 0; i < numbers.length; i++) {
    System.out.println(numbers[i]);
}

6.24. Amaliy misol: user input parse qilish

public class Main {
    public static void main(String[] args) {
        String input = "25";

        try {
            int age = Integer.parseInt(input);

            if (age < 0) {
                throw new IllegalArgumentException("Yosh manfiy bo‘lishi mumkin emas");
            }

            System.out.println("Age: " + age);
        } catch (NumberFormatException e) {
            System.out.println("Yosh faqat raqam bo‘lishi kerak");
        } catch (IllegalArgumentException e) {
            System.out.println(e.getMessage());
        }
    }
}

Agar:

String input = "25";

Natija:

Age: 25

Agar:

String input = "abc";

Natija:

Yosh faqat raqam bo‘lishi kerak

Agar:

String input = "-5";

Natija:

Yosh manfiy bo‘lishi mumkin emas

6.25. Amaliy misol: bank account

public class BankAccount {
    private double balance;

    public BankAccount(double balance) {
        if (balance < 0) {
            throw new IllegalArgumentException("Boshlang‘ich balans manfiy bo‘lishi mumkin emas");
        }

        this.balance = balance;
    }

    public void withdraw(double amount) {
        if (amount <= 0) {
            throw new IllegalArgumentException("Yechiladigan summa musbat bo‘lishi kerak");
        }

        if (amount > balance) {
            throw new IllegalArgumentException("Balans yetarli emas");
        }

        balance -= amount;
    }

    public double getBalance() {
        return balance;
    }
}

Ishlatish:

public class Main {
    public static void main(String[] args) {
        try {
            BankAccount account = new BankAccount(100);

            account.withdraw(30);

            System.out.println("Balance: " + account.getBalance());
        } catch (IllegalArgumentException e) {
            System.out.println("Xato: " + e.getMessage());
        }
    }
}

Natija:

Balance: 70.0

Agar:

account.withdraw(150);

Natija:

Xato: Balans yetarli emas

6.26. Beginner xatolar

Xato 1: Hamma joyda catch (Exception e) yozish

Yomon:

try {
    int number = Integer.parseInt("abc");
} catch (Exception e) {
    System.out.println("Xato");
}

Yaxshi:

try {
    int number = Integer.parseInt("abc");
} catch (NumberFormatException e) {
    System.out.println("Raqam formati noto‘g‘ri");
}

Aniq exception ushlansa, xato sababi tushunarli bo‘ladi.

Xato 2: Exceptionni yutib yuborish

Yomon:

try {
    int result = 10 / 0;
} catch (Exception e) {
}

Yaxshi:

try {
    int result = 10 / 0;
} catch (ArithmeticException e) {
    System.out.println("Nolga bo‘lish mumkin emas");
}

Xato 3: finally ichida return yozish

Yomon amaliyot:

public int test() {
    try {
        return 1;
    } finally {
        return 2;
    }
}

Bu chalkash va xavfli. finallydagi return oldingi returnni bosib ketishi mumkin.

Yaxshi:

public int test() {
    try {
        return 1;
    } finally {
        System.out.println("Cleanup");
    }
}

Xato 4: Exception bilan normal logic qilish

Yomon:

try {
    int value = numbers[10];
} catch (ArrayIndexOutOfBoundsException e) {
    System.out.println("Element yo‘q");
}

Yaxshi:

if (index >= 0 && index < numbers.length) {
    int value = numbers[index];
} else {
    System.out.println("Element yo‘q");
}

Exception oddiy if o‘rniga ishlatilmasligi kerak.

6.27. Qachon try/catch, qachon throw?

6.28. Kichik mashq

Vazifa

Product class yoz:

field:
- name
- price

constructor:
- name null yoki bo‘sh bo‘lsa exception chiqarsin
- price <= 0 bo‘lsa exception chiqarsin

method:
- getInfo() product haqida matn qaytarsin

Yechim:

public class Product {
    private String name;
    private double price;

    public Product(String name, double price) {
        if (name == null || name.isBlank()) {
            throw new IllegalArgumentException("Product name bo‘sh bo‘lishi mumkin emas");
        }

        if (price <= 0) {
            throw new IllegalArgumentException("Product price musbat bo‘lishi kerak");
        }

        this.name = name;
        this.price = price;
    }

    public String getInfo() {
        return name + " = $" + price;
    }
}

Ishlatish:

public class Main {
    public static void main(String[] args) {
        try {
            Product product = new Product("Laptop", 1000);
            System.out.println(product.getInfo());
        } catch (IllegalArgumentException e) {
            System.out.println("Xato: " + e.getMessage());
        }
    }
}

Natija:

Laptop = $1000.0

Agar:

Product product = new Product("", 1000);

Natija:

Xato: Product name bo‘sh bo‘lishi mumkin emas

6.29. Qisqa xulosa

Error handling Java’da xatolarni nazorat qilish uchun kerak:

Exception       → runtime xato
try             → xato chiqishi mumkin bo‘lgan kod
catch           → xatoni ushlash
finally         → baribir ishlaydigan cleanup blok
checked         → compiler majburlaydi
unchecked       → compiler majburlamaydi
throw           → exception chiqarish
throws          → method exception chiqarishi mumkinligini e’lon qilish
custom exception→ o‘zimizning xato turimiz

Eng muhim fikr:

Exception - dasturni yiqitish uchun emas, xatoni nazoratli boshqarish uchun kerak.

Beginner bosqichi shu yerda yakunlanadi. Keyingi katta bo‘lim: Junior → OOP Deep Dive - interfaces, abstract classes, polymorphism, composition over inheritance, encapsulation patterns, inner classes, anonymous classes, enums.