Java Getters, Setters, Data Validation & Controlled Access

class Employee {
    // Private fields
    private final String employeeId; // Read-only: no setter!
    private String name;
    private String email;
    private double salary;
    private boolean active;
    private int[] projectIds;        // Mutable array field

    public Employee(String name, String email, double salary, int[] projectIds) {
        this.employeeId = "EMP-" + System.currentTimeMillis() % 100000;
        setName(name);
        setEmail(email);
        setSalary(salary);
        this.projectIds = projectIds != null ? projectIds.clone() : new int[0];
        this.active = true;
    }

    // GETTERS
    public String getEmployeeId()  { return employeeId; }
    public String getName()        { return name; }
    public String getEmail()       { return email; }
    public double getSalary()      { return salary; }
    public boolean isActive()      { return active; }

    // Defensive copy on getter for mutable array
    public int[] getProjectIds()   { return projectIds.clone(); }

    // Computed (derived) property — no backing field!
    public String getDisplayTitle() {
        return (active ? "[ACTIVE] " : "[INACTIVE] ") + name + " <" + email + ">";
    }

    // SETTERS WITH VALIDATION
    public void setName(String name) {
        if (name == null || name.isBlank())
            throw new IllegalArgumentException("Name cannot be blank.");
        this.name = name.trim();
    }

    public void setEmail(String email) {
        if (email == null || !email.matches("^[\w.-]+@[\w.-]+\.\w{2,}$"))
            throw new IllegalArgumentException("Invalid email format: " + email);
        this.email = email.toLowerCase().trim();
    }

    public void setSalary(double salary) {
        if (salary < 15000)
            throw new IllegalArgumentException("Salary below minimum wage: " + salary);
        if (salary > 5_000_000)
            throw new IllegalArgumentException("Salary exceeds company maximum.");
        this.salary = salary;
    }

    public void setActive(boolean active)      { this.active = active; }
    public void setProjectIds(int[] projectIds) {
        this.projectIds = projectIds != null ? projectIds.clone() : new int[0];
    }

    @Override
    public String toString() {
        return String.format("[%s] %-18s | Salary: $%,9.2f | Active: %b",
                employeeId, name, salary, active);
    }
}

public class Main {
    public static void main(String[] args) {
        System.out.println("=== 1. User Requested BankAccount Pattern Applied to Employee ===");
        Employee emp = new Employee("Ravi Kumar", "ravi.kumar@company.com",
                85000.0, new int[]{101, 205, 312});
        System.out.println(emp);
        System.out.println("Display Title : " + emp.getDisplayTitle());

        System.out.println("
=== 2. Validated Setter Updates ===");
        emp.setSalary(92000.0);
        System.out.println("After raise   : " + emp);

        System.out.println("
=== 3. Setter Validation Guards ===");
        try {
            emp.setSalary(-500.0); // Invalid!
        } catch (IllegalArgumentException e) {
            System.out.println("Salary error  : " + e.getMessage());
        }

        try {
            emp.setEmail("not-an-email"); // Invalid!
        } catch (IllegalArgumentException e) {
            System.out.println("Email error   : " + e.getMessage());
        }

        System.out.println("
=== 4. Defensive Copy Protection ===");
        int[] returnedIds = emp.getProjectIds();
        returnedIds[0] = 9999; // Attempt to corrupt internal array
        System.out.println("Ext. modified [0] : " + returnedIds[0]);
        System.out.println("Internal [0] safe : " + emp.getProjectIds()[0]); // Still 101!

        System.out.println("
=== 5. Computed Property ===");
        emp.setActive(false);
        System.out.println("Inactive title : " + emp.getDisplayTitle());
    }
}

class Temperature {
    private double celsius;

    public Temperature(double celsius) {
        setCelsius(celsius);
    }

    // Setter with physical validation
    public void setCelsius(double celsius) {
        if (celsius < -273.15)
            throw new IllegalArgumentException("Temperature below absolute zero!");
        this.celsius = celsius;
    }

    // Getter for raw value
    public double getCelsius() { return celsius; }

    // Computed getters — derive other scales automatically
    public double getFahrenheit() { return (celsius * 9.0 / 5.0) + 32; }
    public double getKelvin()     { return celsius + 273.15; }

    @Override
    public String toString() {
        return String.format("%.2f°C = %.2f°F = %.2fK", celsius, getFahrenheit(), getKelvin());
    }
}

public class PracticalApplication {
    public static void main(String[] args) {
        Temperature t1 = new Temperature(100.0);
        Temperature t2 = new Temperature(37.0);  // Human body temp

        System.out.println("=== Temperature Converter ===");
        System.out.println("Boiling Point : " + t1);
        System.out.println("Body Temp     : " + t2);

        try {
            new Temperature(-300); // Below absolute zero!
        } catch (IllegalArgumentException e) {
            System.out.println("Physical Error: " + e.getMessage());
        }
    }
}