Section 12 - Object-Orientated Programming - USE NOTES Flashcards
What is a procedural language?
A program consisting of:
- Step-by-step instructions
- Function and procedure calls
- Local and global variables
How does procedural programming work?
Code is broken down into a number of smaller modules, with the program consisting of a series of calls to procedures and functions, each of which may in turn call other procedures or functions
How does object orientated programming work?
The world is viewed as a system of objects, each of which is responsible for its own data and the operations on that data. All processing carried out is done by the objects
What are attributes?
Data that is associated with the class
What features do objects have?
- Attributes
- State
- Behaviours
What are states?
The value of an objects instance variables
What are behaviours?
Actions that can be performed by an object
What is a class?
A blueprint or template for an object that defines the attributes and behaviours of those objects
What is a method?
Attributes and behaviours of an object, they are the functionality of a class
What is a constructor?
Something used to create objects in a class
What are setter methods?
Procedures
What are getter methods?
Functions
What is instantiation?
Where a new object (an instance of a class) is created
Can multiple instances of the same class be created?
Yes, they will share identical methods and attributes, however the value of their attributes will be unique to each instance
What is a reference type variable?
Variables that hold a pointer or reference to where the object itself is stored
What is a variable reference diagram?
A graphical form showing how objects are referenced by reference variables
What is an instance of a class?
Objects created from that class
What is encapusaltion?
All the data and methods of an object are combined into a single entity so that the attributes or behaviours of one object cannot affect the way in which another object functions
What is a subclass?
A “child” class in object-orientated programming
Why do programmers use encapsulation?
- Different programmers can work on different classes and not have to worry about how other parts of the system may affect any code they write
- They can use methods from other classes without having to know how they work
How can you determine whether to use inheritance?
Use the “is a” rule. Ask “is object A an object B?”, and if it is then object A should inherit the data and behaviours from object B
What is a superclass?
A “parent” class in object-orientated programming
What is an inheritance diagram?
A diagram showing the inheritance relationship between different classes
What is inheritance?
Child classes inherit data and behaviours from their parent class
What is association?
A “has a” relationship between classes, meaning there is no ownership between objects and they can be created and deleted independently
What is aggregation?
A more specific interpretation where a class is a collection or container of other classes, however they do not have a lifecycle dependency
What is composition?
A stronger form of association, where if the container object is destroyed then every instance of the contained class is also destroyed
How is aggregation shown in class diagrams?
A hollow diamond shape next to the container object
How is composition shown in class diagrams?
A filled in diamond shape next to the container object
What is polymorphism?
A programming languages ability to process objects differently depending on their class.
What is overriding?
Defining a method with the same name and formal argument types as a method inherited from a superclass
Why is composition favoured over inheritence?
- It allows for greater flexibility as composition is a less rigid relationship between the 2 objects
- An object may be composed of several other objects but cannot be said in a real-world sense to “inherit” their characteristics
What is information hiding?
Where the objects instance variables are hidden so other objects must use messages to interact with that object’s state
What are the 3 access modifiers?
- Public
- Private
- Protected
What can access a method/instance variable that has been declared public?
Code within any class
What can access a method/instance variable that has been declared private?
Code within the class itself can access it
What can access a method/instance variable that has been declared protected?
The definition varies between languages, however the most common definitions are only members of the same subclass, and only members in the same package/library of classes
What is an interface?
A collection of abstract methods that a group of unrelated classes may implement
What is the advantage of using an interface?
New classes can be added which use the interface without affecting existing classes
What is the point of encapsulating what varies?
It reduces maintenance and testing effort
What is encapsulating what varies?
When something changes in a program, if the concept in question is encapsulated in a single module then only that module needs to change
What are the advantages of OOP?
- The object-orientated methodology forces programmers to go through extensive planning, making better designs with less weaknesses
- Encapsulation means that source code for an object can be written, tested and maintained independently of the code for other objects
- Once an object is created, knowledge of how its methods are implemented is no necessary for it to be used
- New objects with small differences to existing ones can be created easily
- Objects that are already defined, coded and tested can be reused in other programs
- An object-orientated program is much easier to maintain because of its modular structure
