Object-Oriented Programming

Question 1

What are the major programming paradigms?

Answer 1

Imperative
–uses statements to change a program’s state

Declarative
–describes the desired result, system figures out how to achieve it

Question 2

What are the tyes of imperative programming? (3)

Answer 2

• Procedural
• OOP
• Recursive Programming

Question 3

What are the tyes of declarative programming? (3)

Answer 3

• Functional Programming
• Logic Programming
• Constraint Programming

Question 4

What type of programming does Python use?
What about java?

Answer 4

-tends toward functional, but supports procedural and object-oriented
-primarily object-oriented, but added constructs to allow
functional programming

Question 5

Describe the features of objects (3, one depends on the language)

Answer 5

An object:
–collects together related data (“fields”, “attributes”)
–collects together subroutines to work on that data (“methods”, “member functions”, etc.)
–may (depending on the language) allow hiding the data members and/or function members, restricting access to them to its subroutines only

Question 6

What are the features of OOP languages? (5)

Answer 6

Encapsulation
– related data and procedures are kept together, and data or even
procedures may be hidden from outside access
Classes (definition of data/procedures)
– class variables (belong to the class as a whole, e.g. “static” in Java)
Objects (instances of a Class)
– instance variables (belong to a particular object)
Composition
– objects can contain other objects as members
Inheritance or Delegation

Question 7

What is not a defining feature of OOP but almost always present?

Answer 7

Inheritance

Question 8

What is inheritance?

Answer 8

means that a subclass can use subroutines or data members defined in an ancestor class

Question 9

What is delegation?

Answer 9

means that a member of an object (“receiver”) is evaluated in the context of some other object (“sender”)
– can be done by passing the sender to the receiver as a parameter

Question 10

Describe polymorphism? What allows it?

Answer 10

Polymorphism
– Inheritance allows Polymorphism
– a single function call in the source code can invoke different functions at runtime depending on the type of the object
– implemented by having a table of function pointers associated withevery object (one table per class)

Question 11

What is SOLID?

Answer 11

Acronym for five principles of Object-Oriented Design
– SRP: Single Responsibility Principle
– OCP: Open/Closed Principle
– LSP: Liskov Substitution Principle
– ISP: Interface Segregation Principle
– DIP: Dependency Inversion Principle

Question 12

What is a singleton?

Answer 12

A class which never has more than a single object instantiated

Question 13

How do you implement a singleton? (2)

Answer 13

1. hiding the class constructor –
2. providing a static function that returns the sole instanc

Question 14

What’s an adapter? (1)

Answer 14

Convert the interface of a class to look like another class’s interface

Question 15

• What’s an iterator? (1)
• How is it implemented?

Answer 15

• allows traversal of a container object and accessing the container’s elements
• typically implemented as a class with functions such as init(), next(), and getItem()

Question 16

What are the benefits of an iterator? (2)

Answer 16

• avoids exposing the container’s data structure
• can define new traversal operations without changing container’s interface (algorithms and containers are decoupled by iterators)

Question 17

For python, what are two supported functions and one other entity related to iterating class objects?

Answer 17

• it = obj.__iter__() return an iterator object
• (often self) – it.__next__() get next item
• raise StopIteration if no next item

Question 18

What is the “Strategy” design pattern? (3)

Answer 18

• instead of “class Foo extends Bar” [Java] or class Foo(Bar) [Python], Foo has a member of type Bar which it invokes as needed
• this allows runtime selection of behavior
• The Strategy pattern decouples behaviors from the classes that use the behaviors

Example: Java’s “interface”/”implements” are a form of this design pattern

Question 19

Give an example of something that implements the strategy design pattern

Answer 19

– Java’s “interface”/”implements” are a form of this design pattern

Question 20

What’s a useful way to think of when to use inheritance?

Answer 20

think of inheritance as “is-substitutable-for”, not “is-a” (Liskov substitution principle)

Question 21

What’s an interface?

Answer 21

An interface is a programming structure/syntax that allows the computer to enforce certain properties on an object (class) (e.g. methods)

Question 22

DIP – Dependency Inversion Principle (2) How is it achieved? (idea and term for it)

Answer 22

● High-level modules should not depend on low-level modules; both should depend on abstractions

● Abstractions should not depend on details; details should depend on abstractions

● Achieved by not directly instantiating dependencies (i.e. no “new MyDependency()” anywhere in the class)

– typically use Dependency Injection (in its basic form, an instance of the dependent class is passed in by the caller)

Question 23

What’s polymorphism?

Answer 23

objects of different types can be accessed through the same interface. Each type can provide its own, independent implementation of this interface

Question 24

What’s the test for a polymorphic object?

Answer 24

If the object successfully passes multiple is-a or instanceof tests, it’s polymorphic. As I’ve described in my post about inheritance, all Java classes extend the class Object. Due to this, all objects in Java are polymorphic because they pass at least two instanceof checks.

Question 25

Describe the concept of factories

Answer 25

Use a factory object and a factory method

• a Factory Object is an object that can create other objects
• a Factory Method is a method of an object (or class) which returns new instances of one or more classes

Question 26

Are constructors polymorphic? What about factories?

Answer 26

• constructors are not polymorphic
• factories can be polymorphic – a single function could return objects of multiple different types

Question 27

What’s an abstract factory?

Answer 27

A class does not create objects itself, but instead delegates the creation to another class which is specified at run-time