Cosc346 - Object Oriented Programming

Front 1

What is abstraction?

Back 1

Abstraction is when knowledge of the inner workings of a project is not required to use it.

Front 2

What it encapsulation?

Back 2

Encapsulation is the ability to control access to the inner state of the object.

Front 3

What is interchangeability?

Back 3

Interchangeability is the ability to change the inner workings in an object without affecting its interface and code depending on it.

Front 4

What are constructors?

Back 4

These are special methods which are always invoked upon creation. This is the place where the internal state if the object can be initialised. They typically carry the same name as the class and can take parameters, which allow user-defined initialisation.

Front 5

What are destructors?

Back 5

Destructors are methods that are automatically invoked upon object destruction.

Front 6

What are instance variables?

Back 6

Variables where values may differ for different objects of a given class.

Front 7

What are class variables?

Back 7

Variables which are shared by all objects of a given class.

Front 8

What are instance methods?

Back 8

Methods invoked on an object, Typically depend on (read or write) the values of instance variables. The message is sent to the object.

Front 9

What are class methods?

Back 9

Methods that can be used without creating an object, cannot depend on instance variables. The message is sent to the class.

Front 10

What happens when you create an object

instance?

Back 10

First, you create an object reference/pointer, then you create an object instance and set the

reference value so it points to the address where

the object is located.

Front 11

What happens when you assign an object reference to another reference?

Back 11

Two references point to the same object instance - operation through either reference changes the state of the object.

Front 12

What happens when you create a copy of an object?

Back 12

Create a new object instance and copy the values of all instance variables.

Front 13

What happens when you assign an object copy to another copy?

Back 13

Two references point to different object instances - operation through one reference does not affect another object associated with the other reference.

Front 14

What is a shallow copy?

Back 14

A shallow copy only copies it's reference.

Front 15

What is a deep copy?

Back 15

A deep copy creates a new instance of the internal object and copies the state.

Front 16

What is inheritance?

Back 16

Inheritance is the creation of a subclass from a previously existing class. It allows us to re-use code by adding new methods, modifying or overriding existing methods i.e is-a relationship.

Front 17

What are subclasses and superclasses?

Back 17

Subclasses extend superclasses, methods are inherited by subclasses along with instance variables.

Front 18

Why use inheritance?

Back 18

Specialisation - subclass is a more specialised form of its parent.

Specification - subclass implements behaviour described, but not implemented by its parent.

Extension - subclass provides new behaviour and capabilities.

Limitation - subclass restricts behaviour of parent class.

Generalisation - subclass modifies behaviour of parent.

Front 19

What is private view?

Back 19

Not accessible outside the code that implements class.

Front 20

What is public view?

Back 20

Accessible by object user and the subclass implementation

Front 21

What is protected view?

Back 21

Variables and methods of the parent are accessible from code implementing subclass, but not by the object user.

Front 22

What is overriding (inheritance)?

Back 22

When a subclass can implement a method already defined/implemented by its superclass.

Front 23

What is multiple inheritance?

Back 23

A scenario where a subclass as multiple parents.

Front 24

Why don't many languages support multiple inheritance?

Back 24

Diamond of Death. If one subclass has multiple parents, it wont know which one to inherit.

Front 25

What is composition?

Back 25

Composition is where a class includes another class as its instance variable i.e. has-a relationship.

Front 26

What are the benefits of inheritance?

Back 26

Code reusability - no need to implement methods inherited from parent.

Interface consistency - easy to conform to generic requirement for an interface while implementing only few methods.

Code portability - low level routines (superclasses at the top of the tree) can be used in different projects.

Front 27

What are the costs of inheritance?

Back 27

Weakens encapsulation - need to understand how the superclass works in order to uses the subclass.

Execution speed - especially at initialisation time, when a series of constructors(initialisation routines) gets invoked.

Memory usage.

Front 28

Inheritance vs Composition?

Back 28

There should be little need of subclassing [of this class]. If you need to customise behaviour, is it often better to consider composition instead of subclassing.

Front 29

What is mandatory inheritance?

Back 29

When initialising, it is important to call the initialisation method of the superclass before doing anything to the instance variables

Front 30

What is single inheritance?

Back 30

A class can extend only one superclass - it can only have one parent.

Front 31

What is a stack?

Back 31

A stack is typically used for arguments and local variables within functions and variables.

The stack is a part of memory that is managed Last-In-First-Out.

Front 32

What is a heap?

Back 32

A heap is used for objects and large/persistent

data structures such as C arrays. The heap is a part of memory that is managed more generically.

Front 33

What is automatic reference counting?

Back 33

It is when the compiler keeps track of objects and figures out when to release them when they are no longer needed.

Front 34

What is manual reference counting?

Back 34

Is it when you explicitly free up(deallocate) any memory that you allocated to the heap.

Front 35

What is garbage collection?

Back 35

Garbage collection is when the run-time environment scans through your program and removes objects that aren't being used.

Front 36

What is a weak reference?

Back 36

A weak reference is when the object gets created, it has a retain count of 0.

Front 37

What is a strong reference?

Back 37

A strong reference is when the object gets created, it has a retain count of 1. It is the default behaviour for object pointers.

Front 38

What is overloading (polymorphism)?

Back 38

Is is when a method or function has the same name but different implementations for different numbers of parameters or parameter types.

Front 39

What is overriding (polymorphism)?

Back 39

Overriding refers to the ability to send the same message to instances of different classes. The methods operate in different ways but provide analogous behaviour. The internal behaviour may differ but the external interface is the same.

Front 40

What is static typing?

Back 40

A data type that is derived from variable definition. Static typing is more readable and allows compiler to do error-checking.

Front 41

What is a polymorphic variable?

Back 41

A variable that can hold values of different types.

e.g. id, super, self.

Front 42

What is dynamic typing?

Back 42

A data type that is derived from its value. Data typing is more flexible but you must do error-checking.

Front 43

What is dynamic binding?

Back 43

Run-time determination of which method to use is called dynamic binding.

Front 44

What are generics?

Back 44

Also referred to parametric polymorphism, templates provide ability to operate on generic data types.

Front 45

What is coupling?

Back 45

Coupling is how much different components of a system, such as objects in a program depend on each other.

Front 46

What is cohesion?

Back 46

Cohesion is how well components, such as instance variables of the class belong together.

Front 47

What are the 7 steps of object-oriented design?

Back 47

1. Requirements - first understand the problem in terms of requirements.

2. Use cases - next understand how the system might be used to perform a particular task.

3. Determine classes - often suggested by use cases.

4. CRC cards - how the classes interact.

5. Assigning responsibilities - to classes.

6. Sequence diagrams - dynamic interaction between classes.

7. Class diagrams - static interaction between classes.

Front 48

Object oriented design patterns.

(try to remember at least 5)

Back 48

Creating Objects:

1. A software factory provides the ability to make objects.

2. A singleton class insures only one instance of the class exist.

Object Structure:

1. A composite object is a combination of different objects.

2. An adapter allows objects with incompatible interfaces to interact.

3. A proxy provides an interface with a server.

4. A facade farms out work to multiple objects.

Object Behaviour:

1. The chain of responsibility selects appropriate object for a message.

2. A command encapsulates messages for queues etc.

3. A mediator manages communication between loosely coupled objects.

4. An observer patter allows loose communication from on-to-many.

5. An iterator allows enumeration of objects in a collection.

Front 49

What is an event loop?

Back 49

It waits for events from the OS and dispatches them to appropriate handlers.

Front 50

What is XIB?

Back 50

"Xcode/XML Interface Builder" - The xml file in your project that contains description of all visual components added in the interface builder.

Front 51

What is NIB?

Back 51

The compile code corresponding to the XIB file. A binary file that saves all the objects corresponding to the AppKits classes specified in the XIB file.

Front 52

UI Design Patterns.

(try to remember atleast 5)

Back 52

Safe Exploration - undo/redo, back/forward

Instant Gratification - predict the first thing users want to do.

Satisficing - satisfying + sufficing, "this is good enough. I dont want to spend more time learning to do it better."

Changes in Midstream - Don't lock users into interactions they have to finish.

Deferred Choices -“I don’t want to answer that now; just let me finish!”.

Incremental Construction - creative activities require incremental improvements and constant testing.

Habituation - Consistency across applications and within applications.

Spatial Memory - Keep buttons and tools in the same relative location withing your application.

Prospective Memory - Provide flexibility to allow users to implement their own reminder system.

Streamlined Repetition - Automate repetitive tasks.

Keyboard Only - Implement keyboard alternative to most application functionality.

Front 53

UI Content Organisation Patterns.

Back 53

Two-Panel Selector

Canvas + Palette

One-Window Drilldown

Alternative Views

Wizards

Extras on demand

Multi-Level Help

Front 54

Navigation Patterns.

Back 54

Clear Entry Points - few options on startup.

Global Navigation - Repeated motif/toolbar on each window.

Hub and Spoke - organises discrete task from central hub.

Pyramid - use back/next/up to organise documents.

Modal Panel - dialog box that must be resolved now.

Sequence Map - "you are here" indicator in a sequence.

Breadcrumbs - for hierarchies, show parent pages.

Annotated Scrollbar - provide information in scrollbar.

Colour-coded sections - use colour to identify locations.

Animated Transition - Show next location by animation.

Escape Hatch - cancel current action.

Front 55

Gestalt Principles.

Back 55

Proximity - Things close together are associated.

Similarity - Things of the same shape, size, colour or orientation are associated.

Continuity - Things which together form lines and curves are associated.

Closure - Simple closed forms like rectangles or white space are associated, even if actual rectangles aren't drawn.

Front 56

UI Layout Design Patterns.

Back 56

Visual Framework - consistency between windows/dialogs in your application.

Central Stage - Make the most important window large.

Title Sections - categories with obvious titles.

Card Stack - use tabs to organise information.

Closable Panels - tabs that that can dynamically size.

Movable Panels - let users move panels around the window.

Right/left alignment - align columns to provide vertical lines.

Diagonal Balance - balance from top left to bottom right.

Responsive Disclosure - show only what needs to be shown.

Responsive Enabling - allow only relevant responses.

Liquid Layout - change window contents during resize