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Test-Driven Development in Java

Solution: Transforming Shape Area Calculation

Explore how to apply TDD and SOLID principles by refactoring shape area calculation in Java. Understand creating abstract classes, overriding methods, and designing flexible, extensible code that calculates combined areas of multiple shapes.

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Let’s understand how we have refactored the code for the “Transforming Shape Area Calculation” exercise.

Java
abstract class Shape {
    public abstract double calculateArea();
}
class Rectangle extends Shape {
    private double width;
    private double height;
    public Rectangle(double width, double height) {
        this.width = width;
        this.height = height;
    }
    @Override
    public double calculateArea() {
        return width * height;
    }
}
class AreaCalculator {
    public double calculateTotalArea(Shape[] shapes) {
        double totalArea = 0;
        for (Shape shape : shapes) {
            totalArea += shape.calculateArea();
        }
        return totalArea;
    }
}
public class main {
    public static void main(String[] args) {
        Rectangle[] rectangles = new Rectangle[2];
        rectangles[0] = new Rectangle(5,10);
        rectangles[1] = new Rectangle(3,8);
        AreaCalculator calculator = new AreaCalculator();
        double totalArea = calculator.calculateTotalArea(rectangles);
        System.out.println("Total area: " + totalArea);
    }
}

Code explanation

  • Lines 1–3: We declare an abstract class named Shape with a public abstract method calculateArea(). This method is meant to be implemented by subclasses and will be used to calculate the area ...