Applying Object-Oriented Principles in Complex Tasks

Introduction and Lesson Goal

Today's mission involves using multiple Object-Oriented Programming (OOP) principles to tackle complex tasks. When principles like Encapsulation, Abstraction, Polymorphism, and Composition are blended, the resulting code becomes streamlined and easier to manage. Our goal is to dissect two real-world examples, gaining insights into how these principles can seamlessly orchestrate solutions.

Real-life Example 1: Building an Online Library System

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Real-life Example 2: Building a Shape Drawing Application

Next, we'll develop a shape-drawing application capable of drawing various shapes. For this, we'll employ the principles of Abstraction and Composition.

Abstraction simplifies the complexity associated with drawing different shapes.
Composition takes care of composite shapes.

Here's how we translate these principles into our shape-drawing application:

Java

// Define the basic Shape class
abstract class Shape {
    // Abstract method that will be implemented in each subclass
    public abstract void draw();
}

// Define the Circle class
class Circle extends Shape {
    // Implement the draw method for circle
    @Override
    public void draw() {
        System.out.println("Drawing a circle.");
    }
}

// Define the Square class
class Square extends Shape {
    // Implement the draw method for square
    @Override
    public void draw() {
        System.out.println("Drawing a square.");
    }
}

// Define the ShapeComposite class
class ShapeComposite extends Shape {
    // Initialize with an empty list of shapes
    private ArrayList<Shape> shapes;

    public ShapeComposite() {
        shapes = new ArrayList<Shape>();
    }

    // Add a new shape to the composite
    public void addShape(Shape shape) {
        shapes.add(shape);
    }

    // Implement the draw method to draw each shape in composite
    @Override
    public void draw() {
        for (Shape shape : shapes) {
            shape.draw();
        }
    }
}

public class Main {
    public static void main(String[] args) {
        Circle circle = new Circle();
        Square square = new Square();

        // Drawing individual shapes
        circle.draw();  // Output: Drawing a circle.
        square.draw();  // Output: Drawing a square.

        // Create a ShapeComposite instance for composite shapes
        ShapeComposite compositeShape = new ShapeComposite();

        // Add individual shapes to the composite
        compositeShape.addShape(circle);
        compositeShape.addShape(square);

        // Drawing the composite shape
        compositeShape.draw();
        // Output:
        // Drawing a circle.
        // Drawing a square.
    }
}

// Define the basic Shape class
abstract class Shape {
    // Abstract method that will be implemented in each subclass
    public abstract void draw();
}

// Define the Circle class
class Circle extends Shape {
    // Implement the draw method for circle
    @Override
    public void draw() {
        System.out.println("Drawing a circle.");
    }
}

// Define the Square class
class Square extends Shape {
    // Implement the draw method for square
    @Override
    public void draw() {
        System.out.println("Drawing a square.");
    }
}

// Define the ShapeComposite class
class ShapeComposite extends Shape {
    // Initialize with an empty list of shapes
    private ArrayList<Shape> shapes;

    public ShapeComposite() {
        shapes = new ArrayList<Shape>();
    }

    // Add a new shape to the composite
    public void addShape(Shape shape) {
        shapes.add(shape);
    }

    // Implement the draw method to draw each shape in composite
    @Override
    public void draw() {
        for (Shape shape : shapes) {
            shape.draw();
        }
    }
}

public class Main {
    public static void main(String[] args) {
        Circle circle = new Circle();
        Square square = new Square();

        // Drawing individual shapes
        circle.draw();  // Output: Drawing a circle.
        square.draw();  // Output: Drawing a square.

        // Create a ShapeComposite instance for composite shapes
        ShapeComposite compositeShape = new ShapeComposite();

        // Add individual shapes to the composite
        compositeShape.addShape(circle);
        compositeShape.addShape(square);

        // Drawing the composite shape
        compositeShape.draw();
        // Output:
        // Drawing a circle.
        // Drawing a square.
    }
}

Abstraction: In this example, the Shape class is abstract. We don’t care about the specific details of how each shape is drawn here, but we know that each shape must have a draw() method. The abstract class helps us define this rule for all shapes.
Composition: The ShapeComposite class demonstrates composition by combining multiple shapes. It can hold and draw multiple shapes together. Composition is used when one object (a composite shape) contains other objects (individual shapes).

Applying Object-Oriented Principles in Complex Tasks

Introduction and Lesson Goal

Real-life Example 1: Building an Online Library System

Join the 1M+ learners on CodeSignal

Real-life Example 2: Building a Shape Drawing Application

Lesson Summary