Controlled Access: Getters and Setters

In Object-Oriented Programming, we use the private modifier to hide data from the outside world. This is called Encapsulation. If a variable is public, any part of the program can change it to an invalid state. By making a variable private, we create a 'black box' where the internal data is protected. However, we still need a way to interact with that data safely. This is where Accessors (Getters) and Mutators (Setters) come in. They act as the official interface for your object, ensuring that no one touches the 'raw' data without permission.

A Getter is a method that returns the value of a private variable. It usually follows the naming convention `getVariableName()`. A Setter is a method that updates the value, usually named `setVariableName(newValue)`. Why use these instead of direct access? Because it gives the class control. A getter can format the data before returning it, and a setter can check if the new data is valid before saving it. This prevents the object from entering an 'illegal' state.

The true power of a setter is validation. Before assigning a value to a private field, we can use `if` statements to check if the data makes sense. For example, if we are setting a 'probability' value $P$, we know that mathematically $0 \le P \le 1$. If a user tries to set $P = 1.5$, the setter can reject the change or throw an error. This ensures that the object's internal state always follows the rules of the logic it represents.

Sometimes, getters and setters don't just map to a single variable. They can perform calculations. For instance, a `Circle` class might have a private `radius`. You could create a `getArea()` method that calculates $\pi r^2$ on the fly. Furthermore, you can create a `setArea()` method that actually updates the `radius` by calculating $r = \sqrt{\frac{A}{\pi}}$. This keeps your data synchronized and prevents redundant variables that might get out of sync.