Java Design Patterns Tutorial | Edureka

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TYPES OF DESIGN PATTERNS
STRUCTURE OF DESIGN PATTERNS
WHAT ARE DESIGN PATTERNS?
WHY DO WE NEED DESIGN PATTERNS IN JAVA?
OVERVIEW OF DESIGN PATTERNS

WHY DO WE NEED DESIGN PATTERNS?
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WHY DO WE NEED DESIGN PATTERNS?
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OOP solutions
Easy to Maintain
Efficient

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Software Design Pattern can be defined as a software
template or a description to solve a problem that
occurs in multiple instances while designing a Software
Application or a Software Framework.
DESIGNPATTERN
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Structure of Design Patterns can be described as a graphical representation of the classes
involved in the pattern following the notations of Object Modeling Technique (OMT).
Term Description
Pattern Name Describes the essence of the pattern in a short, but expressive name.
Intent Describes what the Pattern Does
Also, known as List any synonyms of the pattern
Motivation Provides an example of the problem and describes the solution to it
Applicability Lists the situations where the pattern is applicable
Structure Set of diagrams of the classes and objects that depict the pattern
Participants Describes the classes and objects that participate in the design
Collaborations Describes the Participants collaboration and their responsibilities.
Consequences Describes the forces that exist with the pattern and the benefits
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Creational Design Patterns
Structural Design Patterns
Behavioral Design Patterns
JEE Design Patterns
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Creational Design Patterns
Creational Design Patterns are concerned with the method of
creating Objects.
The Creational Design Patterns are classified as follows:
• Factory Design Pattern
• Abstract Factory Pattern
• Singleton Pattern
• Prototype Pattern
• Builder Pattern.
• Object Pool Pattern
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CREATIONAL DESIGN PATTERNS
Factory Design Pattern
Factory Design Pattern: It follows the principle of “Define an interface or
abstract class for creating an object but let the subclasses decide which
class to instantiate“. The Factory Method Pattern is also known as Virtual
Constructor.
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Factory Design Pattern Example
Example: We have three Cellular Network
Plan which describes the call cost per minute.
Here we have three different networks
namely, abcNetwork, pqrNetwork, and
xyzNetwork along with their charges per
minute. Let us find out the cost of a certain
number of minutes on each network.
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Singleton Design Pattern
Singleton Design Pattern: It follows “define a class that has only one
instance and provides a global point of access to it“. The class must ensure
that only a single instance should be created, and a single object can be
used by all other classes.
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Singleton Design Pattern Example
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Example: We have a MySQL Database. Let us
insert data into the database using one single
object instance. Here, we have 4 different
operations that are performed onto the
database and all of those operations use
one single object instance.

Structural Design Patterns
Structural Design Patterns deal with the composition of classes
and objects which form larger structures.
The Structural Design Patterns are further classified as follows:
• Facade Pattern
• Bridge Pattern
• Composite Pattern
• Decorator Pattern
• Adapter Pattern
• Flyweight Pattern
• Proxy Pattern
• Filter Pattern
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STRUCTURAL DESIGN PATTERNS
Facade Design Pattern
Facade Design Pattern: Describes a higher-level interface that makes the
subsystem easier to use. Every Abstract Factory is a Facade Design Pattern.
It protects the end-users from the complex sub-system components.
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Facade Design Pattern Example
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Example: Now, let us use the Facade Design
pattern to find out the cost of the franchise you
wish to buy.

Adapter Design Pattern
Adapter Design Pattern: Provides the interface according to client
requirement while using the services of a class with a different
interface. The Adapter Pattern is also known as Wrapper. It is designed to
enable two or more previously incompatible objects to interact with each
other.
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Adapter Design Pattern Example
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Example: Here is a simple Library Card example
which is designed to issue a Library card to a
new user of the library which includes all the
details like a book holder ID, Account number
and many more. Let us execute this
using Adapter Design Pattern.

Behavioural Design Patterns
Behavior Design Patterns are concerned with the responsibility
and interaction between the objects.
The Behavioural Design Patterns are further classified as follows:
• Strategy Pattern
• Iterator Pattern
• Mediator Pattern
• Command Pattern
• State Pattern
• Observer Pattern
• Template Pattern
• Visitor Pattern
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BEHAVIOURAL DESIGN PATTERNS
Strategy Design Pattern
Strategy Design Pattern: It defines a family of functionality and encapsulates
each one and make them interchangeable. The Strategy Pattern is also known
as Policy.
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Strategy Design Pattern Example
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Example: we are going to consider a simple
example of a calculator. We need to perform five
different operations. We shall encapsulate all
those five operations into Calculator class and
execute the program using the Strategy Design
Pattern.

Command Design Pattern
Command Design Pattern: It encapsulates a request under an object as a
command and passes it to the invoker object. Invoker object looks for the
appropriate object which can handle this command and pass the command
to the corresponding object and that object executes the command. It is
also known as Action or Transaction.
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Command Design Pattern Example
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Example: This example demonstrates a simple
command execution cycle where the user
requires to exhibit switching on and off the
various electronic devices in his houses like
a bulb and stereo player. He invokes the
command through an invoker object called
a simple remote control.

Observer Design Pattern
Observer Design Pattern: It defines a one-to-one dependency so that
when one object changes state, all its dependents are notified and updated
automatically.
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Observer Design Pattern Example
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Example: We are going to execute a program
using the Observer Design Pattern to display
the current average score and the current
predictable score of a cricket match.

JEE Design Patterns
JEE Design Patterns are concerned with providing solutions to the
Java EE-based software applications and frameworks.
The JEE Design Patterns are further classified as follows:
• MVC Design Pattern
• Dependency Injection Pattern
• DAO Design Pattern
• Business Delegate Pattern
• Intercepting Filter Pattern
• Service Locator Pattern
• Transfer Object Pattern
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JEE DESIGN PATTERNS
MVC Design Pattern
MVC Design Pattern: MVC Design Pattern is defined as follows:
• Models are basically objects used as blueprints for all of the objects that
will be used in the application.
• Views are used to represent the presentational aspect of the
information and data located in the models.
• Controllers control and act as both of the Models as well as Views. They
serve as a connection between the Models and Views.
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JEE DESIGN PATTERNS
MVC Design Pattern Example
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Example: We are going to use MVC Design
Pattern to set and print the data of the school
students.

JEE DESIGN PATTERNS
DAO Design Pattern
DAO Design Pattern: DAO is a pattern in which objects are dedicated to the
communication with the Data Layer. These objects instantiate “Session
Factories” and handle all of the logic behind communicating with the
database.
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JEE DESIGN PATTERNS
DAO Design Pattern Example
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Example: We are going display the Developer
details of a certain IT company using the DAO
Design Pattern.

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OVERVIEW OF DESIGN PATTERNS
• They are designed to be reusable in multiple projects.
• Their solutions help to define system architecture with ease.
• Design Patterns can capture the software engineering experiences.
• They provide transparency to the design of an application.
• Design Patterns are well-proven solutions given by Experts.
• Java Design Patterns provide clarity to the System Architecture
• They provide the possibility of building a better system.
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Java Design Patterns Tutorial | Edureka

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