Java Encapsulation

public class BankAccount {    // private fields - hidden from outside    private String owner;    private double balance;    public BankAccount(String owner, double initialBalance) {        this.owner   = owner;        this.balance = (initialBalance >= 0) ? initialBalance : 0;    }    // Getter    public String getOwner() { return owner; }    // Getter with read-only access    public double getBalance() { return balance; }    // Controlled mutation - validation inside setter    public void deposit(double amount) {        if (amount > 0) {            balance += amount;            System.out.printf("Deposited $%.2f. New balance: $%.2f%n", amount, balance);        } else {            System.out.println("Deposit amount must be positive.");        }    }    public void withdraw(double amount) {        if (amount > 0 && amount <= balance) {            balance -= amount;            System.out.printf("Withdrew $%.2f. New balance: $%.2f%n", amount, balance);        } else {            System.out.println("Invalid withdrawal amount.");        }    }    public static void main(String[] args) {        BankAccount acc = new BankAccount("Alice", 1000.0);        System.out.println("Owner: " + acc.getOwner());        acc.deposit(500.0);        acc.withdraw(200.0);        acc.withdraw(2000.0);  // Invalid        // acc.balance = 999999;  // ERROR: balance is private    }}

import java.io.Serializable;public class Student implements Serializable {    private String name;    private int    age;    private double gpa;    private boolean enrolled;    // No-arg constructor (required for JavaBean)    public Student() {}    // Getters    public String  getName()     { return name; }    public int     getAge()      { return age; }    public double  getGpa()      { return gpa; }    public boolean isEnrolled()  { return enrolled; }  // boolean uses 'is'    // Setters with validation    public void setName(String name)       { this.name = name; }    public void setAge(int age)            { if (age > 0) this.age = age; }    public void setGpa(double gpa)         { if (gpa >= 0 && gpa <= 4.0) this.gpa = gpa; }    public void setEnrolled(boolean e)     { this.enrolled = e; }    @Override    public String toString() {        return String.format("Student{name='%s', age=%d, gpa=%.2f, enrolled=%b}",                             name, age, gpa, enrolled);    }    public static void main(String[] args) {        Student s = new Student();        s.setName("Bob");        s.setAge(20);        s.setGpa(3.75);        s.setEnrolled(true);        System.out.println(s);    }}