Geometry Calculator

The problem

Design a Geometry class with the following methods:

A static method that accepts the radius of a circle and returns the area of the circle. Use the following formula:
- Area = π * r * 2
- Use Math.PI for π and r for the radius of the circle
A static method that accepts the length and width of a rectangle and returns the area of the rectangle. Use the following formula:
- Area = Length x Width
A static method that accepts the length of a triangle’s base and the triangle’s height. The method should return the area of the triangle. Use the following formula:
- Area = Base x Height x 0.5

The methods should display an error message if negative values are used for the circle’s radius, the rectangle’s length or width, or the triangle’s base or height.

Next write a program to test the class, which displays the following menu and responds to the user’s selection:

Geometry calculator:

Calculate the Area of a Circle
Calculate the Area of a Rectangle
Calculate the Area of a Triangle
Quit

Enter your choice (1-4):

Display an error message if the user enters a number outside the range of 1 through 4 when selecting an item from the menu.

Breaking it down

Geometry class

public static class Geometry {
    public static double areaOfCircle(double radius) {
        return Math.PI * radius * radius;
    }

    public static double areaOfRectangle(double length, double width) {
        return length * width;
    }

    public static double areaOfTriangle(double base, double h) {
        return base * h * 0.5;
    }
}

Main and user menu choice method

public static void main(String[] args) {

    int choice; // The user's menu choice

    do {
        // Get the user's menu choice.
        choice = getMenu();

        if (choice == 1) {
            calculateCircleArea();
        } else if (choice == 2) {
            calculateRectangleArea();
        } else if (choice == 3) {
            calculateTriangleArea();
        } else if (choice == 4) {
            System.out.println("Thanks for calculating!");
        }

    } while (choice != 4);
}

public static int getMenu() {

    int userChoice;

    // keyboard input
    Scanner keyboard = new Scanner(System.in);

    // Display the menu.
    System.out.println("Geometry Calculator\n");
    System.out.println("1. Calculate the Area of a Circle");
    System.out.println("2. Calculate the Area of a Rectangle");
    System.out.println("3. Calculate the Area of a Triangle");
    System.out.println("4. Quit\n");
    System.out.print("Enter your choice (1-4) : ");

    // get input from user
    userChoice = keyboard.nextInt();

    // validate input
    while (userChoice < 1 || userChoice > 4) {
        System.out.print("Please enter a valid range: 1, 2, 3, or 4: ");
        userChoice = keyboard.nextInt();
    }

    return userChoice;
}

Calculate Circle Area

public static void calculateCircleArea() {

    double radius;

    // Get input from user
    Scanner keyboard = new Scanner(System.in);
    System.out.print("What is the circle's radius? ");
    radius = keyboard.nextDouble();

    // Display output
    System.out.println("The circle's area is "
            + Geometry.areaOfCircle(radius));
}

Calculate Rectangle Area

public static void calculateRectangleArea() {
    double length;
    double width;

    // Get input from user
    Scanner keyboard = new Scanner(System.in);

    // Get length
    System.out.print("Enter length? ");
    length = keyboard.nextDouble();

    // Get width
    System.out.print("Enter width? ");
    width = keyboard.nextDouble();

    // Display output
    System.out.println("The rectangle's area is "
            + Geometry.areaOfRectangle(length, width));
}

Calculate Triangle Area

public static void calculateTriangleArea() {

    double base;
    double height;

    // Get input from user
    Scanner keyboard = new Scanner(System.in);

    // Get the base
    System.out.print("Enter length of the triangle's base? ");
    base = keyboard.nextDouble();

    // Get the height
    System.out.print("Enter triangle's height? ");
    height = keyboard.nextDouble();

    // Display the triangle's area.
    System.out.println("The triangle's area is "
            + Geometry.areaOfTriangle(base, height));
}

Output

Geometry Calculator

1. Calculate the Area of a Circle
2. Calculate the Area of a Rectangle
3. Calculate the Area of a Triangle
4. Quit

Enter your choice (1-4) : 1
What is the circle's radius? 10
The circle's area is 314.1592653589793
Geometry Calculator

1. Calculate the Area of a Circle
2. Calculate the Area of a Rectangle
3. Calculate the Area of a Triangle
4. Quit

Enter your choice (1-4) : 2
Enter length? 10
Enter width? 10
The rectangle's area is 100.0
Geometry Calculator

1. Calculate the Area of a Circle
2. Calculate the Area of a Rectangle
3. Calculate the Area of a Triangle
4. Quit

Enter your choice (1-4) : 3
Enter length of the triangle's base? 10
Enter triangle's height? 10
The triangle's area is 50.0
Geometry Calculator

1. Calculate the Area of a Circle
2. Calculate the Area of a Rectangle
3. Calculate the Area of a Triangle
4. Quit

Enter your choice (1-4) : 4
Thanks for calculating!

Level Up

Geometry calculations are common, examine if there is open source libraries or libraries within the JDK that perform these calculations. What are some reasons why you would to find a common library?
Write unit test for Geometry class