Explain the four pillars of OOP with examples.

1. Encapsulation: Bundling data and methods together, hiding internal details
2. Inheritance: Creating new classes based on existing ones
3. Polymorphism: Same interface, different implementations
4. Abstraction: Hiding complex implementation details

// Encapsulation
public class BankAccount {
    private double balance; // hidden data
    
    public void deposit(double amount) { // controlled access
        if (amount > 0) balance += amount;
    }
}

// Inheritance
class Animal {
    void speak() { System.out.println("Animal speaks"); }
}
class Dog extends Animal {
    void speak() { System.out.println("Woof!"); }
}