Zoo Manifest Code-Along

Update an existing class so that it uses a custom constructor!

Starter App

Open up the starter Zoo Manifest app, and take a look at it.

Animal Class

The Animal class represents an animal. Each Animal has a name, a species, a height (in inches), and a certain number of legs. There is a method that prints this information to the console.

Main Method

First, the main method loops with a while loop, allowing the user to add new Animal objects to the List of animals. After adding animals, the program prints out the information for each Animal object.

Modifications

The goal of this activity is to add a constructor to the Animal class. The actual functionality should NOT change; this is an example of refactoring. This will simplify the code, and make it easier to maintain!

Creating a Constructor

In the Animal.cs file, at the bottom of the class definition, add code for a new custom constructor. Remember, defining a constructor is like defining any other method, with two key differences:

• The name of the constructor has to be the name of the class (in this case, Animal)
• There is no return type for the constructor; instead of returning anything, it initializes a new object of the class type

The code looks like this:

public Animal()
{

}

Constructor Parameters

Now that the skeleton of the constructor has been defined, it's time to make it actually do something!

Developers often use constructors to initialize fields or properties on a class object. To do this for the Animal class, add four parameters to the Animal constructor, each corresponding to one of the fields on the class. The parameters should have the same types as the fields, but they should NOT have the same name.

The code should look something like this:

public Animal(string name, string species, int legs, double heightInCm)
{

}

Setting the Field Values in the Constructor

Now that the constructor has some parameters, the constructor can use them to build the object. This is a lot like setting the field values outside of the constructor, but it makes it easier to initialize objects. In the body of the constructor, set each field to be the parameter value (except for the heightInCm parameter):

Name = name;
Species = species;
NumberOfLegs = legs;

Setting the Height

For the HeightInInches property, things will be a little different. Although it is a little contrived, for this application, the user will always want to enter the height in centimeters, but have it stored in inches. Currently, the Main method converts the height from centimeters to inches before setting the HeightInInches property. Instead, it will be cleaner to do the conversion in the constructor!

Since the height parameter is currently measured in centimeters, set the HeightInInches field to be the value of the heightInCm parameter multiplied by 0.39:

HeightInInches = heightInCm * 0.39;

Now the constructor is complete! That should be all the changes needed in the Animal.cs file.

Using the Constructor

Upon running the project in its current state, an error should appear:

The type `Animal` does not contain a constructor that takes `0` arguments

This is caused by the following statement:

Animal a = new Animal();

Because the Animal class now has a custom constructor, the default constructor no longer exists! This means it is necessary to use the custom constructor when instantiating new Animal objects. Update the code in the main.cs file so that it properly utilizes the Animal constructor.

Passing the Arguments

Now, instead of taking zero arguments, the Animal constructor method takes four. Pass in the name, species, legNum, and heightCm values directly:

Animal a = new Animal(name, species, legNum, heightCm);

Note that it is no longer necessary to convert the heightCm value to inches; that happens in the constructor.

Once this change has been made, remove the direct field setting statements below, as they are no longer required! At this point, the program should work again. Run it, and ensure that it works the same as it did before the changes!