Design Patterns

Question 1

Which pattern is used for 1 to many relationships between objects?

Answer 1

Observer Pattern

Question 2

What are the actors used in observer patterns?

Answer 2

1. Subject
2. Object
3. Client

Question 3

What is a subject(Observable) actor in the Observer pattern?

Answer 3

It holds methods to attach and detach the observers to the client. it is a concrete class that extends the observer class

Question 4

What is an Observer?

Answer 4

The observer is an abstract class with all the methods

Question 5

What are design patterns?

Answer 5

Capture the best practice of experienced object-oriented s/w developers

Question 6

What are the essential elements of patterns?

Answer 6

1. Name
2. Problem and its context
3. Solution with an abstract description
4. Consequences

Question 7

Types of design patterns?

Answer 7

Creational Patterns
Structural Patterns
State Patterns
Command patterns

Question 8

What are creational Patterns?

Answer 8

Create an object for you rather than having you to instantiate an object

Question 9

What are Structural Patterns?

Answer 9

how to group. and organize classes

Question 10

What are state patterns?

Answer 10

Class behavior changes on the basis of State

Question 11

What are the elements of the state pattern?

Answer 11

1. Context
2. State
3. ConcreteState

Question 12

What is Context in state pattern?

Answer 12

The object whose behavior needs to be state-specific
It will have reference to a concrete state, which defines the current state of the context object. The state is proportional to Context.

Question 13

What is State class in State Pattern?

Answer 13

It is implemented as an abstract class/Interface

Question 14

What is a Concrete State in State Pattern?

Answer 14

The class that implements state-specific behavior, have the implementation of setState()

Question 15

What is a Command Pattern?

Answer 15

It is a data-driven design pattern and falls under the behavior pattern category

Question 16

What are the elements of Command Pattern?

Answer 16

1. Interface acts as a command
2. Class that acts as a request.
3. Concrete command classes implementing the interface
4. Class which act as an invoker object.

Question 17

What are Strategy Patterns?

Answer 17

They are used when behavior changes are needed dynamically during runtime

Question 18

What is the intent of Strategy Patterns?

Answer 18

1. Define a group of algorithms that applies to a family of classes
2. Encapsulate each algorithm separately
3. Make the algorithms interchangeable within that family

Question 19

What is the consequence of Strategy Patterns?

Answer 19

The Strategy Pattern lets the specific algorithm implemented by a method vary without affecting the clients that use it.

Question 20

What are the elements of Strategy Patterns?

Answer 20

1. Context
2. Strategy Interface
3. Concrete Strategy classes that implement Strategy Interface

Question 21

What are Adapter Patterns?

Answer 21

It allows the classes to work together with incompatible types

Question 22

What is the intent of Adapter Patterns?

Answer 22

1. Convert the interface of a class into another interface that clients expect.
2. The adapter lets classes work together, which could not otherwise because of incompatible interfaces.

Question 23

What are the elements of the Adapter Pattern?

Answer 23

Target - defines the domain-specific interface that the Client uses.
Adapter - adapts the interface Adaptee to the Target interface.
Adaptee - defines an existing interface that needs adapting.
Client - collaborates with objects conforming to the Target interface.