Structural Design Patterns

Question 1

Provide definition of Adapter pattern

Answer 1

Pattern that allows objects with
incompatible interfaces to collaborate

Question 2

Provide definition of Bridge pattern

Answer 2

Bridge is a structural design pattern that lets you split a large class or a set of closely related classes into two separate
hierarchies—abstraction and implementation—which can be
developed independently of each other

Question 3

What means Abstraction in Bridge pattern

Answer 3

Abstraction (also called interface) is a high-level control layer for some entity. This layer isn’t supposed to do any real work
on its own. It should delegate the work to the implementation layer (also called platform).

Question 4

What means Impelementation in Bridge pattern

Answer 4

An interface or abstract class defining the low-level operational methods. This acts as a base for the concrete implementation

Question 5

Provide definition od Composite pattern

Answer 5

Composite is a structural design pattern that lets you compose objects into tree structures and then work with these structures as if they were individual objects

Question 6

What principle can be violated by Composite pattern and why?

Answer 6

Interface Segregation Principle can violated when Composite definies the methods Add, Remove. They will be empty in the leaf
class. However, the client will be able to treat all the elements equally, even when composing the tree

Question 7

Provide definition for Decorator pattern

Answer 7

Structural design pattern that lets you attach
new behaviors to objects by placing these objects inside special wrapper objects that contain the behaviors

Question 8

What means that inheritance is static

Answer 8

You can’t alter the behavior of an existing
object at runtime. You can only replace the whole object with another one that’s created from a different subclass

Question 9

Which pattern manages the life
cycle of its service object on its own

Answer 9

Proxy

Question 10

Provide definition for Facade pattern

Answer 10

Structural design pattern that provides a simplified interface to a library, a framework, or any other complex set of
classes

Question 11

Facade pattern maigh provide limited functionality

Answer 11

A facade might provide limited functionality in comparison to working
with the subsystem directly. However, it includes only those
features that clients really care about

Question 12

What is the purpose of additional facade

Answer 12

An Additional Facade class can be created to prevent polluting a single facade with unrelated features that might make it yet
another complex structure. Additional facades can be used by
both clients and other facades

Question 13

Provide a definition for Flyweight pattern

Answer 13

Structural design pattern that lets you fit more objects into the available amount of RAM by sharing common parts of state between multiple objects instead of keeping all of the data in each object

Question 14

State of an object with constant data of which lives within the object; other objects can only read it, not change it.

Answer 14

Intrinsic state

Question 15

The object’s state, often altered “from
the outside” by other objects, is called

Answer 15

Extrinsic state

Question 16

What you can say about Flyweight and immutability

Answer 16

You have to make sure that its state can’t be modified.
A flyweight should initialize its state just once, via constructor parameters. It shouldn’t expose any setters or public fields to
other objects.

Question 17

What you can say about Flayweight fatory

Answer 17

It is teh factory method pattern. The method accepts the intrinsic state of the desired flyweight
from a client, looks for an existing flyweight object matching this
state, and returns it if it was found. If not, it creates a new fly-
weight and adds it to the pool

Question 18

Provide a definition for Proxy pattern.

Answer 18

Proxy is a structural design pattern that lets you provide a
substitute or placeholder for another object. A proxy controls
access to the original object, allowing you to perform
something either before or after the request gets through to
the original object

Question 19

What is an alternative implementation of proxy when extracting interface is not possible

Answer 19

Make the proxy a subclass of the service class, and this way it’ll inherit the interface of the service

Question 20

Service class should be passed to Proxy via constructor or should be created internally be Proxy

Answer 20

Usually, proxies create and manage the whole life cycle of their servers. In rare occasions, a service is
passed to the proxy via a constructor by the client