Week 2

Question 1

Name this: “is-a” relationship

Answer 1

Inheritance

Question 2

Name this: “has-a” relationship

Answer 2

Composition

Question 3

Inheritance is determined at _______ time, whereas composition is determined at ___ time

Answer 3

compile, run

Question 4

A subclass if defined in terms of its _________ and can often see the ____________’ internals

Answer 4

superclass. superclass’ internals

Question 5

In composition a class a_________s with others to gain f____________

Answer 5

associates with others to gain functionality

Question 6

Name this: Easy to override methods, can’t change at runtime

Answer 6

Inheritnce

Question 7

Name this: Implementation changes in one level affects its lower level, cascading.

Answer 7

Inheritance

Question 8

Name this: Respects class interface, interfaces need careful design if they are to be used with many other classes

Answer 8

Composition

Question 9

Name this: Encapsulation respected, sometimes more classes needed for a solution (more complex)

Answer 9

Composition

Question 10

For this course: Composition vs Inheritance, which is favoured?

Answer 10

Composition

Question 11

Object 1 has a reference to object 2 and uses that to access methods in object 2. Object 1 is giving the responsibility of operations to object 2.

Who is the delegator, who is the delegate?

Answer 11

Object 1 is the delegator, Object 2 is the delegate

Question 12

Is delegation dynamic? What does that mean? Give an example

Answer 12

Yes it is dynamic, which means it can be changed at runtime. Example: Class “Window” can be a shape other than rectangle.

Question 13

T/F - A delegator may only delegate one delegate object

Answer 13

False. It may delegate multiple delegate objects

Question 14

T/F - Many delegators may use a single delegate

Answer 14

True

Question 15

T/F - A delegate may only expose one method for invocvation

Answer 15

False. It may expose multiple methods for invocation.

Question 16

Name this ex. of delegation in patterns: Object delegates to a “strategy” for its implementation of a method and can change strategies

Answer 16

Strategy

Question 17

Name this ex. of delegation in patterns: Object delegates to another which holds a representation of its
current state

Answer 17

State

Question 18

Name this ex. of delegation in patterns: Object delegates an operation to a “visitor” and that operation is
repeated for each of the object’s structure

Answer 18

Visitor

Question 19

T/F - A “delegate” patterns certainly exists.

Answer 19

False, there is debate over whether it exists

Question 20

T/F - Delegation is a technique or principal

Answer 20

True

Question 21

When is the singleton pattern useful? What are some examples?

Answer 21

When you need to guarantee that only 1 instance is created and used throughout the application. Example would be a database or network connection.

Question 22

The basic approach for the singleton pattern is

_______ constructor
_____ variable
_____ method

Answer 22

Private constructor (Prevent it from being called multiple times),
static variable (Store reference to a single instance),
static method (Returns reference to a single instance)

Question 23

Name this: Ensures a class has one instance and provide a global point of access to it.

Answer 23

Singleton

Question 24

This design pattern separates the construction object from the details of its representation or component objects

Answer 24

Builder

Question 25

This design pattern often has complex objects such as composites or objects composed of multiple objects

Answer 25

Builder

Question 26

What is more flexible, builder pattern or factory pattern?

Answer 26

Builder

Question 27

Explain the 4 steps in the Builders basic approach

Answer 27

1. Uses director class responsible for order and use of build instructions 2. Concrete builder creates the complex object 3. Director adjusts build instructions to obtain different types of objects 4. Director may change the concrete builder to build the same type of object differently

Question 28

T/F - One of the benefits of inheritance is its contributions to encapsulation

Answer 28

False. Inheritance breaks encapsulation, as it exposes the subclass to the details of its parents implementation

Question 29

T/F - Delegation makes composition as powerful for reuse as inheritance

Answer 29

True

Question 30

For the strategy pattern, we let the algorithm vary independently from clients that use it. This is called ______ a____________

Answer 30

Policy applicability

Question 31

When do we apply policy applicability?

Answer 31

When many related classes differ only in there behaviour. It allows us to apply different variants of a given algorithm