Lab: Constructor overloading

Objective

In this exercise, we will explore the concept of constructor overloading in C#. We aim to understand the flexibility and convenience that multiple constructors bring to a class’s instantiation process. We will modify the provided Rectangle class to allow different ways of object creation.

Provided Code

Consider the provided code. Notice how the Rectangle class has two private instance fields but no way to actually set their values. We do have a public method which will help us print Rectangle objects however.

class Rectangle
{
    private double width, height;

    public void Print()
    {
        Console.WriteLine($"({width} x {height})");
    }
}

Rectangle rect = new Rectangle();
rect.Print();

(0 x 0)

Instructions

Let’s enhance the Rectangle class by adding multiple constructors to provide different ways of instantiating rectangle objects.

Step 1: Add a constructor that with two parameters

Let’s begin by adding a constructor with two parameters of type double corresponding to width and height. When you’re done you should be able to execute the following code:

Rectangle rect = new Rectangle(20, 10);
rect.Print();

(20 x 10)

🤔 Reflection

Is it possible to add another constructor with two parameters of type double to the class Rectangle? Why or why not?

Step 2: Add a square constructor

Let’s now add another constructor that only has a single double parameter. This constructor will create a Rectangle object where the width and height are equal, effectively creating a square.

When you’re done with this step you should be able to run the following code:

Rectangle r1 = new Rectangle(20, 10);
r1.Print();

Rectangle r2 = new Rectangle(100);
r2.Print();

(20 x 10)

(100 x 100)

Step 3: Add a copy constructor

Let’s now add a constructor to the Rectangle class that takes another Rectangle object and initializes a new instance with the same dimensions as that rectangle.

When you’re done you should be able to run the following code:

Rectangle r1 = new Rectangle(20, 10);
r1.Print();

Rectangle r2 = new Rectangle(100);
r2.Print();

Rectangle r3 = new Rectangle(r1);
r3.Print();

(20 x 10)

(100 x 100)

(20 x 10)

Step 4: Add a parameterless constructor

Remember how defining a constructor with parameters causes the default parameterless constructor to be removed? Have a look at the error below:

new Rectangle();

Let’s reintroduce a parameterless constructor and choose a sensible default like 1x1. When you’re done you should be able to run the following:

Rectangle r1 = new Rectangle(20, 10);
r1.Print();

Rectangle r2 = new Rectangle(100);
r2.Print();

Rectangle r3 = new Rectangle(r1);
r3.Print();

Rectangle r4 = new Rectangle();
r4.Print();

(20 x 10)

(100 x 100)

(20 x 10)

(1 x 1)

Challenge

Implement a constructor in the Rectangle class that accepts a single string parameter in the format width,height. Your constructor must parse this string to extract the width and height as double values and then initialize the rectangle’s dimensions accordingly.

If the parsing fails due to an invalid format or non-numeric values, your constructor should throw an appropriate exception, like this:

throw new ArgumentException("Could not parse input.");

When you’re done you should be able to run the following code:

Rectangle r1 = new Rectangle(20, 10);
r1.Print();

Rectangle r2 = new Rectangle(100);
r2.Print();

Rectangle r3 = new Rectangle(r1);
r3.Print();

Rectangle r4 = new Rectangle();
r4.Print();

Rectangle r5 = new Rectangle("16.5,9.7");
r5.Print();

Rectangle r6 = new Rectangle("12,hello");

(20 x 10)

(100 x 100)

(20 x 10)

(1 x 1)

(16.5 x 9.7)

System.ArgumentException: Could not parse input.
   at Submission#5.Rectangle..ctor(String dimensions)
   at Submission#11.<<Initialize>>d__0.MoveNext()
--- End of stack trace from previous location ---
   at Microsoft.CodeAnalysis.Scripting.ScriptExecutionState.RunSubmissionsAsync[TResult](ImmutableArray`1 precedingExecutors, Func`2 currentExecutor, StrongBox`1 exceptionHolderOpt, Func`2 catchExceptionOpt, CancellationToken cancellationToken)
   at Submission#5.Rectangle..ctor(String dimensions)
   at Submission#11.<<Initialize>>d__0.MoveNext()
--- End of stack trace from previous location ---
   at Microsoft.CodeAnalysis.Scripting.ScriptExecutionState.RunSubmissionsAsync[TResult](ImmutableArray`1 precedingExecutors, Func`2 currentExecutor, StrongBox`1 exceptionHolderOpt, Func`2 catchExceptionOpt, CancellationToken cancellationToken)

Conclusion

🤔 Reflection

How do the constructors we’ve added enhance the object creation process for the Rectangle class? Reflect on scenarios where each constructor might be the most useful. In a later lab we’ll practice on constructor chaining which makes this process even simpler.

Excellent work! You’ve expanded the Rectangle class functionality by overloading its constructor. In a later lab we’ll practice on constructor chaining which makes this process even simpler.