OOP Exam Style Questions

A taxi firm is investigating replacing its drivers with self-driving cars.
1. Explain why the self-driving system will use a real-time operating system.
  - Self-driving systems need to process input as it is generated, so that they can optimise their route and avoid obstacles; due to their real-time processing of data, they fit the definition of a real-time system.
2. The code for the self-driving system has been written using an object-oriented programming language.
  
  It recognises obstacles in the road and then classifies them.
  The class for Obstacle is shown below.
```
public class Obstacle
    private moving // bool
    private distance //real number in metres
    private direction // int between 1 and 360 (degrees)

    public procedure new(givenMoving, givenDistance, givenDirection)
        moving = givenMoving
        distance = givenDistance
        direction = givenDirection
    endprocedure

    public procedure updateDistance(givenDistance)
        distance = givenDistance
    endprocedure
endclass
```
  1. Write a line of code to create an object called bollard of type Obstacle which is not moving and is 7.8 metres away in a direction of 8 degrees.
    - bollard = new Obstacle(false, 7.8, 8)
  2. Describe an example of encapsulation in the class definition code above.
    - distance is not modifiable directly, only through the class' own updateDistance method
  3. Describe the advantages of using encapsulation.
    - Encapsulation helps prevent a class from being modified in ways which could cause the program to crash or otherwise misbehave
3. The self-driving program recognises people as a special type of obstacle and the class Person should inherit the methods and attributes of Obstacle. People are treated like other obstacles except:
  - When the updateDistance method is called, if the person is more than 2 metres away but is 5 metres (or less) away, the method Controls.beepHorn() is called.
  - When the person is 2 metres away (or closer), the method Controls.applyBrakes() is called as well as Controls.beepHorn()
  Complete the class Person.
  - ```
  class Person inherits Obstacle
      public procedure updateDistance(givenDistance)
          if givenDistance <= 5 then
              Controls.beepHorn()
          endif
          if givenDistance <= 2 then
              Controls.applyBrakes()
          endif
          distance = givenDistance
      endprocedure
  endclass
```
4. Give one advantage and one disadvantage to the customers of the taxi using self-driving cars rather than drivers.
  
  Advantage
  - The customer will likely have a more efficient route, and therefore a faster journey
  Disadvantage
  - The customer may have issues where the car goes to the wrong place, and with no driver to talk to would be unable to correct the destination efficiently
Livid Lizards is a computer game in which players get to fire lizards from a cannon to knock down walls. Players get to pick different types of lizards, each with qualities and special powers.

The game is coded using an object-oriented language. Below is the code for the lizard class:
```
class Lizard
    private speed
    private mass
    private size

    public procedure new(givenSpeed, givenMass, givenSize)
        speed = givenSpeed
        mass = givenMass
        size = givenSize
    endprocedure

    public function breakBlock(brick)
        if speed * mass > brick.getStrength() then
            speed = ((speed * mass) - brick.getStrength()) / mass
            return true
        else
            return false
        endif
    endfunction

    ...
endclass
```
1. Lizard is a class. Describe what is meant by a class.
  - A class is a data structure with methods and attributes used to model a real-world object.
2. Identify an attribute in the Lizard class.
  - speed
3. 1. Describe what is meant by the term inheritance.
    - Inheritance is the process by which a class derives methods and attributes from its superclasses; all methods and attributes from the superclasses are copied into the class, generally with precedence given to the first class in the superclasses; i.e. if two classes define the same method, the first in the inheritance list will give its method to the class.
  2. Explain one way the game's developers might use inheritance for Livid Lizards.
    - Lizards with special powers could be derived from Lizard, inheriting its attributes and methods but being able to override methods for which a special behaviour is wanted.