Hello! Today, we'll venture into the realm of design patterns. Specifically, we'll tackle exercises that apply a single design pattern to problem-solving. Mastering these patterns is a surefire way to extend your coding skills.

Our goal today is to fortify your understanding of when and how to apply specific Object-Oriented Programming (OOP) design patterns. These patterns include Encapsulation, Abstraction, Polymorphism, and Composition.

We'll dissect four real-life scenarios and distinguish which pattern is applicable and why.

Let's get underway!

The Encapsulation pattern proves beneficial for the development of a Database Management System (DBMS). Each DBMS table represents a class, the fields represent private properties, and the functions operating on this data serve as methods.

Encapsulation ensures that data properties are accessed through methods that promote data integrity and prevent inadvertent anomalies. Here's a mini-code snippet to support this concept:

class Employees {
    private val employees = mutableMapOf<Int, String>() // private data property

    fun addEmployee(eid: Int, name: String) { // method to operate on private data
        employees[eid] = name
    }

    fun updateEmployee(eid: Int, newName: String) { // method to operate on private data
        if (employees.containsKey(eid)) {
            employees[eid] = newName
        }
    }

    fun getEmployee(eid: Int): String? { // getter method for private data
        return employees[eid]
    }
}

fun main() {
    val employees = Employees()
    employees.addEmployee(1, "John")
    employees.addEmployee(2, "Mark")

    employees.updateEmployee(2, "Jake")

    println(employees.getEmployee(1)) // Outputs: John
    println(employees.getEmployee(2)) // Outputs: Jake
}

In this context, Encapsulation restricts direct access to employee data, presenting a protective layer via designated methods.

When transitioning to GUI development, consider the creation of controls like buttons or checkboxes. Despite belonging to the same parent class, each responds differently when clicked. This situation illustrates Polymorphism, which allows us to handle different objects uniformly via a common interface.

Check out this illustrative example:

open class Control {
    open fun click() {
        // method that can be overridden
    }
}

class Button : Control() {
    override fun click() {
        println("Button Clicked!") // overridden method
    }
}

class CheckBox : Control() {
    override fun click() {
        println("CheckBox Clicked!") // overridden method
    }
}

fun main() {
    val b: Control = Button()
    val c: Control = CheckBox()

    // Click Controls
    b.click() // Outputs: Button Clicked!
    c.click() // Outputs: CheckBox Clicked!
}

Despite sharing the common click interface, different controls display unique responses. This characteristic demonstrates Polymorphism.