Practice Questions — Encapsulation and Access Modifiers

public class Student {
    private String name;
    private int age;
    private double marks;

    public Student(String name, int age, double marks) {
        this.name = name;
        setAge(age);
        setMarks(marks);
    }

    public String getName() { return name; }
    public int getAge() { return age; }
    public double getMarks() { return marks; }

    public void setAge(int age) {
        if (age < 5 || age > 100) throw new IllegalArgumentException("Invalid age: " + age);
        this.age = age;
    }

    public void setMarks(double marks) {
        if (marks < 0 || marks > 100) throw new IllegalArgumentException("Marks must be 0-100: " + marks);
        this.marks = marks;
    }

    public String toString() {
        return name + ", age " + age + ", marks " + marks;
    }

    public static void main(String[] args) {
        Student s = new Student("Aarav", 20, 92.5);
        System.out.println(s);
        try { s.setAge(-5); } catch (IllegalArgumentException e) { System.out.println("Error: " + e.getMessage()); }
        try { s.setMarks(150); } catch (IllegalArgumentException e) { System.out.println("Error: " + e.getMessage()); }
    }
}

public class BankAccount {
    private String accountHolder;
    private double balance;

    public BankAccount(String accountHolder, double initialBalance) {
        this.accountHolder = accountHolder;
        this.balance = initialBalance;
    }

    public String getAccountHolder() { return accountHolder; }
    public double getBalance() { return balance; }

    public void deposit(double amount) {
        if (amount <= 0) throw new IllegalArgumentException("Amount must be positive");
        balance += amount;
        System.out.printf("Deposited Rs.%.2f | Balance: Rs.%.2f%n", amount, balance);
    }

    public void withdraw(double amount) {
        if (amount <= 0) throw new IllegalArgumentException("Amount must be positive");
        if (amount > balance) {
            System.out.println("Error: Insufficient funds");
            return;
        }
        balance -= amount;
        System.out.printf("Withdrew Rs.%.2f | Balance: Rs.%.2f%n", amount, balance);
    }

    public String toString() {
        return String.format("%s: Rs.%.2f", accountHolder, balance);
    }

    public static void main(String[] args) {
        BankAccount acc = new BankAccount("Priya", 10000);
        System.out.println(acc);
        acc.deposit(5000);
        acc.withdraw(3000);
        acc.withdraw(20000);
    }
}

final class DateInfo {
    private final int day;
    private final int month;
    private final int year;

    public DateInfo(int day, int month, int year) {
        if (month < 1 || month > 12) throw new IllegalArgumentException("Invalid month");
        if (day < 1 || day > 31) throw new IllegalArgumentException("Invalid day");
        if (year < 1) throw new IllegalArgumentException("Invalid year");
        this.day = day;
        this.month = month;
        this.year = year;
    }

    public int getDay() { return day; }
    public int getMonth() { return month; }
    public int getYear() { return year; }

    public boolean isLeapYear() {
        return (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0);
    }

    @Override
    public String toString() {
        return String.format("%02d/%02d/%04d", day, month, year);
    }

    public static void main(String[] args) {
        DateInfo d1 = new DateInfo(15, 8, 2026);
        System.out.println(d1);
        System.out.println("Leap year: " + d1.isLeapYear());

        DateInfo d2 = new DateInfo(29, 2, 2024);
        System.out.println(d2);
        System.out.println("Leap year: " + d2.isLeapYear());
    }
}

class Vehicle {
    public String publicField = "public";
    protected String protectedField = "protected";
    String defaultField = "default";
    private String privateField = "private";

    void sameClassAccess() {
        System.out.println("Same class: " + publicField + ", " + protectedField + ", " + defaultField + ", " + privateField);
    }
}

class SamePackageClass {
    void access() {
        Vehicle v = new Vehicle();
        System.out.println("Same package: " + v.publicField + ", " + v.protectedField + ", " + v.defaultField);
        // v.privateField — NOT accessible
        System.out.println("private: NOT accessible from same package");
    }
}

public class Main {
    public static void main(String[] args) {
        Vehicle v = new Vehicle();
        v.sameClassAccess();
        new SamePackageClass().access();
    }
}

final class Employee {
    private final String name;
    private final String department;
    private final double salary;
    private final boolean isRemote;

    Employee(String name, String department, double salary, boolean isRemote) {
        this.name = name;
        this.department = department;
        this.salary = salary;
        this.isRemote = isRemote;
    }

    public String getName() { return name; }
    public String getDepartment() { return department; }
    public double getSalary() { return salary; }
    public boolean isRemote() { return isRemote; }

    public String toString() {
        return "Employee{name='" + name + "', department='" + department + "', salary=" + salary + ", remote=" + isRemote + "}";
    }
}

class EmployeeBuilder {
    private String name;
    private String department = "General";
    private double salary;
    private boolean isRemote = false;

    public EmployeeBuilder setName(String name) { this.name = name; return this; }
    public EmployeeBuilder setDepartment(String dept) { this.department = dept; return this; }
    public EmployeeBuilder setSalary(double salary) { this.salary = salary; return this; }
    public EmployeeBuilder setRemote(boolean remote) { this.isRemote = remote; return this; }

    public Employee build() {
        if (name == null || name.isEmpty()) throw new IllegalArgumentException("Name required");
        if (salary <= 0) throw new IllegalArgumentException("Salary must be positive");
        return new Employee(name, department, salary, isRemote);
    }

    public static void main(String[] args) {
        Employee e = new EmployeeBuilder()
            .setName("Deepak")
            .setDepartment("Engineering")
            .setSalary(75000)
            .setRemote(true)
            .build();
        System.out.println(e);
    }
}

record Product(String name, double price, int quantity) {
    Product {
        if (price <= 0) throw new IllegalArgumentException("Price must be positive");
        if (quantity < 0) throw new IllegalArgumentException("Quantity cannot be negative");
    }

    double totalValue() {
        return price * quantity;
    }

    boolean isInStock() {
        return quantity > 0;
    }
}

public class Main {
    public static void main(String[] args) {
        Product p1 = new Product("Laptop", 50000.0, 10);
        System.out.println(p1);
        System.out.println("Total value: " + p1.totalValue());
        System.out.println("In stock: " + p1.isInStock());

        Product p2 = new Product("Keyboard", 1500.0, 0);
        System.out.println(p2);
        System.out.println("In stock: " + p2.isInStock());
    }
}