project: Assessment: Classes and objects

Tags technical-assessment skill/classes_and_objects

Note about submission format

On Tilde you will notice that this card is asking for a link submission. Please don’t worry about submitting a link. You will be assessed according to TOPIC: Introduction to live assessments

You need to prove that you understand the following concepts:

  • how constructors work
  • construction of multiple class instances:
  • make many objects of the same class
  • interact with them and see that they are distinct
  • getters and setters
  • inheritance and overriding and extending methods
  • composition

Python

Constructors

The constructor is a method that is called when an object is created. This method is defined in the class and can be used to initialize basic variables. In Python the __init__() method is called in place of the constructor - to instantiate (initialise) the object.

class Rectangle:
  def __init__(self, length, width):
    ...

The learner should know how to create an initialiser that takes in arguments and create instance variables.

Instantiation

The learner should be able to instantiate the object.

rectangle = Rectangle(2,4)

The learner should also understand how multiple instances of an object work.

small_rectangle1 = Rectangle(2, 4)
small_rectangle2 = Rectangle(2, 4)
medium_rectangle = Rectangle(4, 12)

Inheritance

The learner should know what is inheritance and what it means when a class inherits another class. Both single and multiple inheritances should be understood, and the use of super() in both cases.

class Square(Rectangle):
  pass

class Cuboid(Rectangle):
  def __init__(self, length, width, height):
      super().__init__(length, width)
      self.height = height

Overriding

The learner should know how to override a function using super and without using super.

Java

Constructors

The learner should know that the constructor name must be the same as its class name.

class Rectangle{

    Rectangle(){
      ....
    }

The learner should know that a single class can have multiple constructors with different numbers of parameters.

class Rectangle{
    ....

    // no arg constructor
    Rectangle()
    ....

    // parameterized constructor
    Rectangle(double length, double width)
    ....

Instantiation

The learner should know how to instantiate a class object.

  Rectangle rectangle1 = new Rectangle();
  Rectangle rectangle2 = new Rectangle(10.0, 6.0);
  Rectangle rectangle2 = new Rectangle(6.0, 7.0);

Inheritance

The learner must know that to inherit from a class, the keyword extends is used.

class Square extends Rectangle { .... }

class Cuboid extends Rectangle {
  private double length, width, height;

  public Cuboid(double length, double width, double height) {
    super(length, width);
    this.length = height;
  }
  ....
}

Overriding

Learner should know that constructors and methods declared with final or static cannot be overridden. If a method cannot be inherited, it cannot be overridden.

Javascript

Constructors

Learner should know how constructors work

class Rectangle {
  constructor(length, width){
    this.length = length
    this.width = width
  }
}

Instantiation

Learner should know how to instantiate many objects from the same class and interact with them

const smallRectangle1 = new Rectangle(2, 4)
const smallRectangle2 = new Rectangle(2, 4)
const mediumRectangle = new Rectangle(4, 12)


console.log(smallRectangle1.length) //2
console.log(mediumRectangle.width) //12

Inheritance and overriding

Learner should understand inheritance and overriding and extending methods

class Rectangle {
  ...
  details(){
    return `The length of the rectangle is ${this.length}, and the width is ${this.width}`;
  }
}

class Cuboid extends Rectangle {
  constructor(length, width){
    super();
  };
  details(){
    return `The length of the cuboid is ${this.length}, and the width is ${this.width}`;
  };
};

The learner should know that constructors and methods declared with final or static cannot be overridden. If a method cannot be inherited, it cannot be overridden.

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