What are public methods? What are private methods?

Public methods are the methods of a class that can be accessed from any other class or any instance of that class. They act as an interface between the class and anything that interacts with it. When a programmer defines a public method, they are essentially defining how other parts of the code (or even separately written code) can use and interact with that class.

Private methods, on the other hand, are only accessible within the class they are defined in. They are used for internal operations of the class and are not intended to be accessed from other classes or instances. Private methods are used to enforce encapsulation, a principle in OOP that emphasizes hiding implementation details of a class from other parts of the code to make it easier to maintain and prevent unwanted interference.

Let's consider an example in Java. Suppose a class named 'BankAccount' is created to represent a bank account. ```java public class BankAccount { private double balance; public BankAccount(double initialBalance) { this.balance = initialBalance; } public void deposit(double amount) { this.balance += amount; } public void withdraw(double amount) { if (amount > this.balance) { System.out.println("Insufficient funds"); return; } this.balance -= amount; } private void updateBalance(double newBalance) { this.balance = newBalance; } } ``` In this example, 'deposit()' and 'withdraw()' are public methods that can be accessed by other classes or instances to perform transactions with the bank account. But 'updateBalance()' is a private method, meaning it is only accessible within the 'BankAccount' class. It is an internal operation that should not be accessed by other parts of the code.

In summary, public methods are accessible to other classes to interact with instances of that class, whereas private methods are used internally within the class for internal operations. Public methods are the way external users and developers interact with the class, while private methods promote encapsulation and keep implementation details hidden from other code. Understanding the difference between public and private methods is crucial when designing and using OOP code.