Question

Look at the following pseudocode class definitions: Class Vegetable Public Module message() Display "I'm a vegetable." End Module End Class Class Potato Extends Vegetable Public Module message() Display "I'm a potato." End Module End Class Given these class definitions, what will the following pseudocode display? Declare Vegetable v Declare Potato p Set v = New Potato() Set p = New Potato() Call v.message() Call p.message()

Short answer

Answer: The output of the given pseudocode will be: I'm a potato. I'm a potato.

Step-by-step solution

Analyze Class Definitions

First, analyze the given class definitions: We have "Class Vegetable" with a public module (method) named "message", which displays "I'm a vegetable.", and "Class Potato" which extends "Class Vegetable". This means that the Potato class inherits properties and methods of the Vegetable class. In this case, Class Potato also has a public module named "message" which displays "I'm a potato." Since Potato class has its own implementation of "message" method, it overrides the inherited method from Vegetable class.

Declare Objects

Now, we will analyze the given pseudocode sequence. Two objects are declared with variable names 'v' and 'p'. 'v' is a variable of the type Vegetable and 'p' is a variable of type Potato. The code then proceeds to create new objects for both the variables using 'New' keyword.

Create Objects

The code then creates objets for the declared variables: 1. Set v = New Potato(): A new object of "Potato" class is created and assigned to the 'v' variable. Even though 'v' is of type 'Vegetable', it can hold a reference to the 'Potato' object as Potato is a subclass of Vegetable 2. Set p = New Potato(): A new object of "Potato" class is created and assigned to the 'p' variable.

Call Methods

At this point, we have two objects with variable names 'v' and 'p'. Now, the pseudocode calls the "message()" method on both objects: 1. Call v.message(): Since 'v' is referencing an object of type 'Potato' which has its own 'message()' method implementation, it will execute that method and display "I'm a potato." 2. Call p.message(): The 'p' object is also an instance of "Potato" class, so it will execute the same 'message()' method in the Potato class and display "I'm a potato."

Output

Based on the analysis, the output of the given pseudocode will be: I'm a potato. I'm a potato.

Key concepts

Object-Oriented Programming

Object-Oriented Programming (OOP) is a programming paradigm that uses 'objects' and 'classes' to create models based on the real world. An object is a self-contained component that contains properties and methods needed to make a certain type of data useful. For example, in our pseudocode, 'Potato' and 'Vegetable' can be considered as objects. A class, on the other hand, is like a blueprint for an object, defining what properties and methods the objects will have.

Classes encapsulate data for the object and methods to manipulate that data. OOP allows for better organization of code, makes it easier to handle complexity by breaking down problems into more manageable pieces, and improves maintainability and reusability of code.

Class Inheritance

Class inheritance is a feature of object-oriented programming that allows a class to inherit properties and methods from another class, known as the parent or superclass. In the pseudocode provided, 'Class Potato' extends 'Class Vegetable', which means that 'Potato' inherits the 'message' method from 'Vegetable'. It allows for the creation of a new class with pre-existing properties and methods, facilitating code reusability and the creation of a hierarchical relationship between classes.

Inheritance promotes the concept of code reusability by allowing a new class to borrow methods and properties from existing classes. As in our example, the 'Potato' therefore has access to the 'message' method originally defined in the 'Vegetable' class.

Method Overriding

Method overriding happens when a subclass or child class has a method with the same name, and parameters as a method in its superclass. The subclass's version of the method overrides the superclass's version. When you call the overridden method on an object, which method executes depends on the actual class of the object.

In our pseudocode, when we call 'v.message()', 'v' is a reference of type 'Vegetable', but it points to an object of type 'Potato'. Due to method overriding, the output is 'I'm a potato.' and not 'I'm a vegetable.' because the 'message' method of the 'Potato' class overrides the 'message' method in the 'Vegetable' class.

Polymorphism

Polymorphism is a core concept in OOP that allows objects to be treated as instances of their parent class rather than their actual class. The term 'polymorphism' comes from the Greek words 'poly', meaning 'many', and 'morphe', meaning 'forms'. In programming, it refers to the ability of different objects to respond uniquely to the same method call.

In the context of our exercise, polymorphism is demonstrated with the 'v.message()' command. Here, 'v' is a 'Vegetable' type, but because it points to a 'Potato' object, it takes the form of a 'Potato' when 'v.message()' is called. This flexibility is what makes polymorphism a powerful feature in OOP, allowing for more generic and abstract coding, which leads to better scalability and easier maintenance.