Design Patterns Reference Guide
Content
Design Patterns Reference Guide
Design Patterns Reference Guide
Explained
Creational Patterns
Pattern
Definition
Abstract
Factory
Provide an
interface for
creating
families of
related or
dependent
objects
without
specifying
their concrete
classes.
Participants
AbstractFactory
declares an interface for
operations that create
abstract products
ConcreteFactory
implements the operations to
create concrete product
objects
AbstractProduct
declares an interface for a
type of product object
Product
defines a product object to
be created by the
corresponding concrete
factory
implements the
AbstractProduct interface
Client
uses interfaces declared by
AbstractFactory and
AbstractProduct classes
UML Class Diagram
Frequency of Usage, Benefits and
Usage
High
Benefits
- Isolates concrete classes
- Allows to change product family easily
Promotes consistency among products
Usage
- When the system needs to be independent of how
its products are created composed and represented.
- When the system needs to be configured with one
of multiple families of products.
- When a family of products need to be used together
and this constraint needs to be enforced.
- -When you need to provide a library of products,
expose their interfaces not the implementation.
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Design Patterns Reference Guide
Factory
Method
Singleton
Define an
interface for
creating an
object, but let
subclasses
decide which
class to
instantiate.
Factory
Method lets a
class defer
instantiation to
subclasses.
Ensure a
class has only
one instance
and provide a
global point of
access to it.
Product
defines the interface of objects
the factory method creates
ConcreteProduct
implements the Product
interface
Creator
declares the factory method,
which returns an object of type
Product. Creator may also
define a default implementation
of the factory method that
returns a default
ConcreteProduct object.
may call the factory method to
create a Product object.
ConcreteCreator
overrides the factory method to
return an instance of a
ConcreteProduct.
Singleton
defines an Instance operation
that lets clients access its unique
instance. Instance is a class
operation.
responsible for creating and
maintaining its own unique
instance.
High
Benefits
Eliminates the needs to bind application classes into
your code. The code deals woth interfaces so it can
work with any classes that implement a certain
interface.
Enables the subclasses to provide an extended
version of an object, because creating an object inside
a class is more flexible than creating an object
directly in the client.
Usage
When a class cannot anticipate the class of objects it
must create.
When a class wants its subclasses to specify the
objects it creates.
Classes delegate responsability to one of several
helper subclasses, and you want to localize the
knowledge of which helper subclasses is the delegate.
medium high
Benefits
Controlled access to unique instance.
Reduced name space.
Allows refinement of operations and representations.
Permits a variable number of instances.
More flexible than class operations.
Usage
When there must be only one instance of a class.
Structural Patterns
Pattern
Definition
Participants
UML Class Diagram
Frequency of Usage, Benefits and
Usage
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Design Patterns Reference Guide
Adapter
Convert the
interface of a
class into
another
interface
clients expect.
Adapter lets
classes work
together that
couldn't
otherwise
because of
incompatible
interfaces
Composit Compose
objects into
e
tree structures
to represent
part-whole
hierarchies.
Composite
lets clients
treat individual
objects and
compositions
of objects
uniformly.
Target
defines the domain-specific
interface that 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.
Component
declares the interface for
objects in the composition.
implements default
behavior for the interface
common to all classes, as
appropriate.
declares an interface for
accessing and managing its
child components.
(optional) defines an
interface for accessing a
component's parent in the
recursive structure, and
implements it if that's
appropriate.
Leaf
represents leaf objects in
the composition. A leaf has
medium high
Benefits
Allow two or more incompatible objects to
communicate and interact.
Improves reusability of older functionality.
Usage
When you want to use an existing class, and its
interface does not match the interface you need.
When you want to create a reusable class that
cooperates with unrelated or onforeseen classes,
classes that don't necesarily have compatible
interfaces.
When you want to use an object in an environment
that expects an interface that is diferent from the
object's interface.
When you must ensure interface translation among
multiple sources.
medium high
Benefits
Define class hierarchies consisting of primitive
objects and composite objects.
Makes it easier to add new kind of components.
Provides flexibility of structure and manageable
interface.
Usage
When you want to represent the whole hierarchy or a
part of the hierarchy of objects.
When you want clients to be able to ignore the
differences between compositions of objects and
individual objects.
When the structure can have any level of complexity
andis dynamic.
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Design Patterns Reference Guide
no children.
defines behavior for
primitive objects in the
composition.
Composite
defines behavior for
components having
children.
stores child components.
implements child-related
operations in the
Component interface.
Client
manipulates objects in the
composition through the
Component interface.
Decorato
r
Attach
additional
responsibilitie
s to an object
dynamically.
Decorators
provide a
flexible
alternative to
subclassing
for extending
functionality.
Component
defines the interface for
objects that can have
responsibilities added to
them dynamically.
ConcreteComponent
defines an object to which
additional responsibilities
can be attached.
Decorator
maintains a reference to a
Component object and
defines an interface that
conforms to Component's
interface.
ConcreteDecorator
adds responsibilities to the
Medium
Benefits
More flexibility than static inheritance.
Avoids feature-laedn classes high up in the hierarchy.
Simplifies coding because you write a series of
classes each targeted at a specific part of the
functionality rather than coding all behavior into the
object.
Enhances the object's extensibility because you make
changes by coding new classes.
Usage
When you want to add responsibilities to individual
objects dinamically and transparently, without
affecting other objects.
When you want to add responsibilities to the object
that you might want to change in the future.
When extension by static subclassing is impractical.
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Design Patterns Reference Guide
Facade
Provide a
unified
interface to a
set of
interfaces in a
subsystem.
Façade
defines a
higher-level
interface that
makes the
subsystem
easier to use.
component.
Facade
knows which subsystem
classes are responsible for
a request.
delegates client requests to
appropriate subsystem
objects.
Subsystem classes
implement subsystem
functionality.
handle work assigned by
the Facade object.
have no knowledge of the
facade and keep no
reference to it.
High
Benefits
Provides a simple interface to a complex system
without reducing the functionality provided by the
system.
Shields clients from complexity of subsystem
components.
Promotes weak coupling between the subsystem and
its clients.
Reduces coupling between subsystems if every
subsystem uses its own facade pattern.
Translates client requests to the subsystems that can
fulfill those requests.
Usage
When you want to provide a simple interface to a
complex subsystem.
When there are many dependencies between clients
and the implementation classes of an abstraction.
When you want to layer your subsystems.
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Design Patterns Reference Guide
Proxy
Provide a
surrogate or
placeholder
for another
object to
control access
to it.
Proxy
maintains a reference
that lets the proxy
access the real subject.
Proxy may refer to a
Subject if the
RealSubject and
Subject interfaces are
the same.
provides an interface
identical to Subject's
so that a proxy can be
substituted for for the
real subject.
controls access to the
real subject and may
be responsible for
creating and deleting
it.
other responsibilites
depend on the kind of
proxy:
remote proxies are
responsible for
encoding a request and
its arguments and for
sending the encoded
request to the real
subject in a different
address space.
medium high
Benefits
A remote proxy can hide the fact that an object
resides in a different address space.
A virtual proxy can perform optimizations such as
creating an object on demand.
both protection proxies and smart references allow
additional housekeeping tasks when an object is
accessed.
Usage
when you need a more versatile or sophisticated
reference to an object than a simple pointer.
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Design Patterns Reference Guide
virtual proxies may
cache additional
information about the
real subject so that
they can postpone
accessing it. For
example, the
ImageProxy from the
Motivation caches the
real images's extent.
protection proxies
check that the caller
has the access
permissions required
to perform a request.
Subject
defines the common
interface for RealSubject
and Proxy so that a Proxy
can be used anywhere a
RealSubject is expected.
RealSubject
defines the real object that
the proxy represents.
Behavioral Patterns
Pattern
Definition
Participants
UML Class Diagram
Frequency of Usage
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Design Patterns Reference Guide
Command Encapsulate a
request as an
object,
thereby letting
you
parameterize
clients with
different
requests,
queue or log
requests, and
support
undoable
operations.
Command
declares an interface for
executing an operation
ConcreteCommand
defines a binding between
a Receiver object and an
action
implements Execute by
invoking the
corresponding operation(s)
on Receiver
Client
creates a
ConcreteCommand object
and sets its receiver
Invoker
asks the command to carry
out the request
Receiver
knows how to perform the
operations associated with
carrying out the request.
medium high
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Design Patterns Reference Guide
Iterator
Observer
Provide a way
to access the
elements of
an aggregate
object
sequentially
without
exposing its
underlying
representation
.
Iterator
defines an interface for
accessing and traversing
elements.
ConcreteIterator
implements the Iterator
interface.
keeps track of the current
position in the traversal of
the aggregate.
Aggregate
defines an interface for
creating an Iterator object
ConcreteAggregate
implements the Iterator
creation interface to return
an instance of the proper
ConcreteIterator
Define a oneSubject
to-many
knows its observers. Any
dependency
number of Observer
between
objects so that objects may observe a
subject
when one
object
provides an interface for
changes
attaching and detaching
state, all its
Observer objects.
dependents
ConcreteSubject
are notified
stores state of interest to
and updated
automatically. ConcreteObserver
sends a notification to its
observers when its state
high
high
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Design Patterns Reference Guide
State
Allow an
object to alter
its behavior
when its
internal state
changes. The
object will
appear to
change its
class.
changes
Observer
defines an updating
interface for objects that
should be notified of
changes in a subject.
ConcreteObserver
maintains a reference to a
ConcreteSubject object
stores state that should
stay consistent with the
subject's
implements the Observer
updating interface to keep
its state consistent with the
subject's
Context
defines the interface of
interest to clients
maintains an instance of a
ConcreteState subclass
that defines the current
state.
State
defines an interface for
encapsulating the behavior
associated with a
particular state of the
Context.
Concrete State
each subclass implements
medium
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Design Patterns Reference Guide
Strategy
Define a
family of
algorithms,
encapsulate
each one, and
make them
interchangeab
le. Strategy
lets the
algorithm vary
independently
from clients
that use it.
a behavior associated with
a state of Context
Strategy
declares an interface
common to all supported
algorithms. Context uses
this interface to call the
algorithm defined by a
ConcreteStrategy
ConcreteStrategy
implements the algorithm
using the Strategy
interface
Context
is configured with a
ConcreteStrategy object
maintains a reference to a
Strategy object
may define an interface
that lets Strategy access its
data.
medium high
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Design Patterns Reference Guide
Template
Define the
skeleton of an
algorithm in
an operation,
deferring
some steps to
subclasses.
Template
Method lets
subclasses
redefine
certain steps
of an
algorithm
without
changing the
algorithm's
structure.
AbstractClass
defines abstract
primitive operations
that concrete
subclasses define to
implement steps of an
algorithm
implements a template
method defining the
skeleton of an
algorithm. The
template method calls
primitive operations as
well as operations
defined in
AbstractClass or those
of other objects.
ConcreteClass
implements the
primitive operations to
carry out subclassspecific steps of the
algorithm
medium
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Design Patterns Reference Guide
Summary
Creational Patterns
Abstract
Factory
Builder
Factory
Method
Prototype
Singleton
Creates an instance of several families of
classes
Separates object construction from its
representation
Creates an instance of several derived
classes
A fully initialized instance to be copied or
cloned
A class of which only a single instance can
exist
Structural Patterns
Adapter
Bridge
Composite
Match interfaces of different classes
Separates an object’s interface from its
implementation
A tree structure of simple and composite
objects
Decorator
Add responsibilities to objects dynamically
Facade
A single class that represents an entire
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Design Patterns Reference Guide
subsystem
Flyweight
Proxy
A fine-grained instance used for efficient
sharing
An object representing another object
Behavioral Patterns
Chain of
Resp.
Command
Interpreter
Iterator
Mediator
Memento
Observer
State
A way of passing a request between a
chain of objects
Encapsulate a command request as an
object
A way to include language elements in a
program
Sequentially access the elements of a
collection
Defines simplified communication between
classes
Capture and restore an object's internal
state
A way of notifying change to a number of
classes
Alter an object's behavior when its state
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Design Patterns Reference Guide
changes
Strategy
Encapsulates an algorithm inside a class
Template
Defer the exact steps of an algorithm to a
Method
Visitor
subclass
Defines a new operation to a class without
change
OO Basics
Abstraction
Encapsulation
Polymorphism
Inheritance
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Design Patterns Reference Guide
OO Design Principles
Encapsulate what varies.
Favor composition over inheritance.
Program to interfaces, not implementations.
Strive for loosely coupled designs between objects that interact.
Classes should be open for extension but closed for modification.
Depend on abstractions. Do not depend on concrete classes.
Only talk to your friends.
Don’t call us, we’ll call you.
A class should have only one reason to change.
References:
Head First Design Patterns –
http://www.javainterview.com/design_patterns_interview_questions.html
http://www.java-interview.com/design_patterns_interview_questions.html
http://www.apwebco.com/gofpatterns/
http://www.java-interview.com/design_patterns_interview_questions.html
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Design Patterns Reference Guide
Explained
Creational Patterns
Pattern
Definition
Abstract
Factory
Provide an
interface for
creating
families of
related or
dependent
objects
without
specifying
their concrete
classes.
Participants
AbstractFactory
declares an interface for
operations that create
abstract products
ConcreteFactory
implements the operations to
create concrete product
objects
AbstractProduct
declares an interface for a
type of product object
Product
defines a product object to
be created by the
corresponding concrete
factory
implements the
AbstractProduct interface
Client
uses interfaces declared by
AbstractFactory and
AbstractProduct classes
UML Class Diagram
Frequency of Usage, Benefits and
Usage
High
Benefits
- Isolates concrete classes
- Allows to change product family easily
Promotes consistency among products
Usage
- When the system needs to be independent of how
its products are created composed and represented.
- When the system needs to be configured with one
of multiple families of products.
- When a family of products need to be used together
and this constraint needs to be enforced.
- -When you need to provide a library of products,
expose their interfaces not the implementation.
1
Design Patterns Reference Guide
Factory
Method
Singleton
Define an
interface for
creating an
object, but let
subclasses
decide which
class to
instantiate.
Factory
Method lets a
class defer
instantiation to
subclasses.
Ensure a
class has only
one instance
and provide a
global point of
access to it.
Product
defines the interface of objects
the factory method creates
ConcreteProduct
implements the Product
interface
Creator
declares the factory method,
which returns an object of type
Product. Creator may also
define a default implementation
of the factory method that
returns a default
ConcreteProduct object.
may call the factory method to
create a Product object.
ConcreteCreator
overrides the factory method to
return an instance of a
ConcreteProduct.
Singleton
defines an Instance operation
that lets clients access its unique
instance. Instance is a class
operation.
responsible for creating and
maintaining its own unique
instance.
High
Benefits
Eliminates the needs to bind application classes into
your code. The code deals woth interfaces so it can
work with any classes that implement a certain
interface.
Enables the subclasses to provide an extended
version of an object, because creating an object inside
a class is more flexible than creating an object
directly in the client.
Usage
When a class cannot anticipate the class of objects it
must create.
When a class wants its subclasses to specify the
objects it creates.
Classes delegate responsability to one of several
helper subclasses, and you want to localize the
knowledge of which helper subclasses is the delegate.
medium high
Benefits
Controlled access to unique instance.
Reduced name space.
Allows refinement of operations and representations.
Permits a variable number of instances.
More flexible than class operations.
Usage
When there must be only one instance of a class.
Structural Patterns
Pattern
Definition
Participants
UML Class Diagram
Frequency of Usage, Benefits and
Usage
2
Design Patterns Reference Guide
Adapter
Convert the
interface of a
class into
another
interface
clients expect.
Adapter lets
classes work
together that
couldn't
otherwise
because of
incompatible
interfaces
Composit Compose
objects into
e
tree structures
to represent
part-whole
hierarchies.
Composite
lets clients
treat individual
objects and
compositions
of objects
uniformly.
Target
defines the domain-specific
interface that 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.
Component
declares the interface for
objects in the composition.
implements default
behavior for the interface
common to all classes, as
appropriate.
declares an interface for
accessing and managing its
child components.
(optional) defines an
interface for accessing a
component's parent in the
recursive structure, and
implements it if that's
appropriate.
Leaf
represents leaf objects in
the composition. A leaf has
medium high
Benefits
Allow two or more incompatible objects to
communicate and interact.
Improves reusability of older functionality.
Usage
When you want to use an existing class, and its
interface does not match the interface you need.
When you want to create a reusable class that
cooperates with unrelated or onforeseen classes,
classes that don't necesarily have compatible
interfaces.
When you want to use an object in an environment
that expects an interface that is diferent from the
object's interface.
When you must ensure interface translation among
multiple sources.
medium high
Benefits
Define class hierarchies consisting of primitive
objects and composite objects.
Makes it easier to add new kind of components.
Provides flexibility of structure and manageable
interface.
Usage
When you want to represent the whole hierarchy or a
part of the hierarchy of objects.
When you want clients to be able to ignore the
differences between compositions of objects and
individual objects.
When the structure can have any level of complexity
andis dynamic.
3
Design Patterns Reference Guide
no children.
defines behavior for
primitive objects in the
composition.
Composite
defines behavior for
components having
children.
stores child components.
implements child-related
operations in the
Component interface.
Client
manipulates objects in the
composition through the
Component interface.
Decorato
r
Attach
additional
responsibilitie
s to an object
dynamically.
Decorators
provide a
flexible
alternative to
subclassing
for extending
functionality.
Component
defines the interface for
objects that can have
responsibilities added to
them dynamically.
ConcreteComponent
defines an object to which
additional responsibilities
can be attached.
Decorator
maintains a reference to a
Component object and
defines an interface that
conforms to Component's
interface.
ConcreteDecorator
adds responsibilities to the
Medium
Benefits
More flexibility than static inheritance.
Avoids feature-laedn classes high up in the hierarchy.
Simplifies coding because you write a series of
classes each targeted at a specific part of the
functionality rather than coding all behavior into the
object.
Enhances the object's extensibility because you make
changes by coding new classes.
Usage
When you want to add responsibilities to individual
objects dinamically and transparently, without
affecting other objects.
When you want to add responsibilities to the object
that you might want to change in the future.
When extension by static subclassing is impractical.
4
Design Patterns Reference Guide
Facade
Provide a
unified
interface to a
set of
interfaces in a
subsystem.
Façade
defines a
higher-level
interface that
makes the
subsystem
easier to use.
component.
Facade
knows which subsystem
classes are responsible for
a request.
delegates client requests to
appropriate subsystem
objects.
Subsystem classes
implement subsystem
functionality.
handle work assigned by
the Facade object.
have no knowledge of the
facade and keep no
reference to it.
High
Benefits
Provides a simple interface to a complex system
without reducing the functionality provided by the
system.
Shields clients from complexity of subsystem
components.
Promotes weak coupling between the subsystem and
its clients.
Reduces coupling between subsystems if every
subsystem uses its own facade pattern.
Translates client requests to the subsystems that can
fulfill those requests.
Usage
When you want to provide a simple interface to a
complex subsystem.
When there are many dependencies between clients
and the implementation classes of an abstraction.
When you want to layer your subsystems.
5
Design Patterns Reference Guide
Proxy
Provide a
surrogate or
placeholder
for another
object to
control access
to it.
Proxy
maintains a reference
that lets the proxy
access the real subject.
Proxy may refer to a
Subject if the
RealSubject and
Subject interfaces are
the same.
provides an interface
identical to Subject's
so that a proxy can be
substituted for for the
real subject.
controls access to the
real subject and may
be responsible for
creating and deleting
it.
other responsibilites
depend on the kind of
proxy:
remote proxies are
responsible for
encoding a request and
its arguments and for
sending the encoded
request to the real
subject in a different
address space.
medium high
Benefits
A remote proxy can hide the fact that an object
resides in a different address space.
A virtual proxy can perform optimizations such as
creating an object on demand.
both protection proxies and smart references allow
additional housekeeping tasks when an object is
accessed.
Usage
when you need a more versatile or sophisticated
reference to an object than a simple pointer.
6
Design Patterns Reference Guide
virtual proxies may
cache additional
information about the
real subject so that
they can postpone
accessing it. For
example, the
ImageProxy from the
Motivation caches the
real images's extent.
protection proxies
check that the caller
has the access
permissions required
to perform a request.
Subject
defines the common
interface for RealSubject
and Proxy so that a Proxy
can be used anywhere a
RealSubject is expected.
RealSubject
defines the real object that
the proxy represents.
Behavioral Patterns
Pattern
Definition
Participants
UML Class Diagram
Frequency of Usage
7
Design Patterns Reference Guide
Command Encapsulate a
request as an
object,
thereby letting
you
parameterize
clients with
different
requests,
queue or log
requests, and
support
undoable
operations.
Command
declares an interface for
executing an operation
ConcreteCommand
defines a binding between
a Receiver object and an
action
implements Execute by
invoking the
corresponding operation(s)
on Receiver
Client
creates a
ConcreteCommand object
and sets its receiver
Invoker
asks the command to carry
out the request
Receiver
knows how to perform the
operations associated with
carrying out the request.
medium high
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Design Patterns Reference Guide
Iterator
Observer
Provide a way
to access the
elements of
an aggregate
object
sequentially
without
exposing its
underlying
representation
.
Iterator
defines an interface for
accessing and traversing
elements.
ConcreteIterator
implements the Iterator
interface.
keeps track of the current
position in the traversal of
the aggregate.
Aggregate
defines an interface for
creating an Iterator object
ConcreteAggregate
implements the Iterator
creation interface to return
an instance of the proper
ConcreteIterator
Define a oneSubject
to-many
knows its observers. Any
dependency
number of Observer
between
objects so that objects may observe a
subject
when one
object
provides an interface for
changes
attaching and detaching
state, all its
Observer objects.
dependents
ConcreteSubject
are notified
stores state of interest to
and updated
automatically. ConcreteObserver
sends a notification to its
observers when its state
high
high
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Design Patterns Reference Guide
State
Allow an
object to alter
its behavior
when its
internal state
changes. The
object will
appear to
change its
class.
changes
Observer
defines an updating
interface for objects that
should be notified of
changes in a subject.
ConcreteObserver
maintains a reference to a
ConcreteSubject object
stores state that should
stay consistent with the
subject's
implements the Observer
updating interface to keep
its state consistent with the
subject's
Context
defines the interface of
interest to clients
maintains an instance of a
ConcreteState subclass
that defines the current
state.
State
defines an interface for
encapsulating the behavior
associated with a
particular state of the
Context.
Concrete State
each subclass implements
medium
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Design Patterns Reference Guide
Strategy
Define a
family of
algorithms,
encapsulate
each one, and
make them
interchangeab
le. Strategy
lets the
algorithm vary
independently
from clients
that use it.
a behavior associated with
a state of Context
Strategy
declares an interface
common to all supported
algorithms. Context uses
this interface to call the
algorithm defined by a
ConcreteStrategy
ConcreteStrategy
implements the algorithm
using the Strategy
interface
Context
is configured with a
ConcreteStrategy object
maintains a reference to a
Strategy object
may define an interface
that lets Strategy access its
data.
medium high
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Design Patterns Reference Guide
Template
Define the
skeleton of an
algorithm in
an operation,
deferring
some steps to
subclasses.
Template
Method lets
subclasses
redefine
certain steps
of an
algorithm
without
changing the
algorithm's
structure.
AbstractClass
defines abstract
primitive operations
that concrete
subclasses define to
implement steps of an
algorithm
implements a template
method defining the
skeleton of an
algorithm. The
template method calls
primitive operations as
well as operations
defined in
AbstractClass or those
of other objects.
ConcreteClass
implements the
primitive operations to
carry out subclassspecific steps of the
algorithm
medium
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Design Patterns Reference Guide
Summary
Creational Patterns
Abstract
Factory
Builder
Factory
Method
Prototype
Singleton
Creates an instance of several families of
classes
Separates object construction from its
representation
Creates an instance of several derived
classes
A fully initialized instance to be copied or
cloned
A class of which only a single instance can
exist
Structural Patterns
Adapter
Bridge
Composite
Match interfaces of different classes
Separates an object’s interface from its
implementation
A tree structure of simple and composite
objects
Decorator
Add responsibilities to objects dynamically
Facade
A single class that represents an entire
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Design Patterns Reference Guide
subsystem
Flyweight
Proxy
A fine-grained instance used for efficient
sharing
An object representing another object
Behavioral Patterns
Chain of
Resp.
Command
Interpreter
Iterator
Mediator
Memento
Observer
State
A way of passing a request between a
chain of objects
Encapsulate a command request as an
object
A way to include language elements in a
program
Sequentially access the elements of a
collection
Defines simplified communication between
classes
Capture and restore an object's internal
state
A way of notifying change to a number of
classes
Alter an object's behavior when its state
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Design Patterns Reference Guide
changes
Strategy
Encapsulates an algorithm inside a class
Template
Defer the exact steps of an algorithm to a
Method
Visitor
subclass
Defines a new operation to a class without
change
OO Basics
Abstraction
Encapsulation
Polymorphism
Inheritance
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Design Patterns Reference Guide
OO Design Principles
Encapsulate what varies.
Favor composition over inheritance.
Program to interfaces, not implementations.
Strive for loosely coupled designs between objects that interact.
Classes should be open for extension but closed for modification.
Depend on abstractions. Do not depend on concrete classes.
Only talk to your friends.
Don’t call us, we’ll call you.
A class should have only one reason to change.
References:
Head First Design Patterns –
http://www.javainterview.com/design_patterns_interview_questions.html
http://www.java-interview.com/design_patterns_interview_questions.html
http://www.apwebco.com/gofpatterns/
http://www.java-interview.com/design_patterns_interview_questions.html
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