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Examples of GoF Design Patterns in Java's core ...

2012-06-06 16:59 645 查看

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You can find an overview of a lot design patterns in Wikipedia. It also mentions which patterns are mentioned by GoF. I'll sum them up here and try to assign as much as possible pattern implementations found in both the Java SE and Java EE API's.

Creational patterns

Abstract factory (recognizeable by creational methods returning an abstract/interface type)

java.util.Calendar#getInstance()

java.util.Arrays#asList()

java.util.ResourceBundle#getBundle()

java.net.URL#openConnection()

java.sql.DriverManager#getConnection()

java.sql.Connection#createStatement()

java.sql.Statement#executeQuery()

java.text.NumberFormat#getInstance()

java.lang.management.ManagementFactory

(all

getXXX()

methods)

java.nio.charset.Charset#forName()

javax.xml.parsers.DocumentBuilderFactory#newInstance()

javax.xml.transform.TransformerFactory#newInstance()

javax.xml.xpath.XPathFactory#newInstance()

java.net.URLStreamHandlerFactory#createURLStreamHandler(String)

(Returns singleton object per protocol)

Builder (recognizeable by creational methods returning the instance itself)

java.lang.StringBuilder#append()

(unsynchronized)

java.lang.StringBuffer#append()

(synchronized)

java.nio.ByteBuffer#put()

(also on

CharBuffer

ShortBuffer

IntBuffer

LongBuffer

FloatBuffer

and

DoubleBuffer

)

javax.swing.GroupLayout.Group#addComponent()

All implementations of

java.lang.Appendable

Factory method (recognizeable by creational methods returning a concrete type)

java.lang.Object#toString()

(overrideable in all subclasses)

java.lang.Class#newInstance()

java.lang.Integer#valueOf(String)

(also on

Boolean

Byte

Character

Short

Long

Float

and

Double

)

java.lang.Class#forName()

java.lang.reflect.Array#newInstance()

java.lang.reflect.Constructor#newInstance()

Prototype (recognizeable by creational methods returning a different instance of itself with the same properties)

java.lang.Object#clone()

(the class has to implement

java.lang.Cloneable

)

Singleton (recognizeable by creational methods returning the same instance (usually of itself) everytime)

java.lang.Runtime#getRuntime()

java.awt.Desktop#getDesktop()

Structural patterns

Adapter (recognizeable by creational methods taking an instance of different abstract/interface type and returning an implementation of own/another abstract/interface type which decorates/overrides the given instance)

java.io.InputStreamReader(InputStream)

(returns a

Reader

)

java.io.OutputStreamWriter(OutputStream)

(returns a

Writer

)

javax.xml.bind.annotation.adapters.XmlAdapter#marshal()

and

#unmarshal()

Bridge (recognizeable by creational methods taking an instance of different abstract/interface type and returning an implementation of own abstract/interface type which delegates/uses the given instance)

None comes to mind yet. A fictive example would be

new LinkedHashMap(LinkedHashSet<K>, List<V>)

which returns an unmodifiable linked map which doesn't clone the items, but uses them. The

java.util.Collections#newSetFromMap()

and

singletonXXX()

methods however comes close.

Composite (recognizeable by behavioral methods taking an instance of same abstract/interface type into a tree structure)

java.awt.Container#add(Component)

(practically all over Swing thus)

javax.faces.component.UIComponent#getChildren()

(practically all over JSF UI thus)

Decorator (recognizeable by creational methods taking an instance of same abstract/interface type which adds additional behaviour)

All subclasses of

java.io.InputStream

OutputStream

Reader

and

Writer

have a constructor taking an instance of same type.

java.util.Collections

, the

checkedXXX()

synchronizedXXX()

and

unmodifiableXXX()

methods.

javax.servlet.http.HttpServletRequestWrapper

and

HttpServletResponseWrapper

Facade (recognizeable by behavioral methods which internally uses instances of different independent abstract/interface types)

javax.faces.context.FacesContext

, it internally uses among others the abstract/interface types

LifeCycle

ViewHandler

NavigationHandler

and many more without that the enduser has to worry about it (which are however overrideable by injection).

javax.faces.context.ExternalContext

, which internally uses

ServletContext

HttpSession

HttpServletRequest

HttpServletResponse

, etc.

Flyweight (recognizeable by creational methods returning a cached instance, a bit the "multiton" idea)

java.lang.Integer#valueOf(int)

(also on

Boolean

Byte

Character

Short

Long

Float

and

Double

)

Proxy (recognizeable by creational methods which returns an implementation of given abstract/interface type which in turn delegates/uses a different implementation of given abstract/interface type)

java.lang.reflect.Proxy

java.rmi.*

, the whole API actually.

The Wikipedia example is IMHO a bit poor, lazy loading has actually completely nothing to do with the proxy pattern at all.

Behavioral patterns

Chain of responsibility (recognizeable by behavioral methods which (indirectly) invokes the same method in another implementation of same abstract/interface type in a queue)

java.util.logging.Logger#log()

javax.servlet.Filter#doFilter()

Command (recognizeable by behavioral methods in an abstract/interface type which invokes a method in an implementation of a different abstract/interface type which has been encapsulated by the command implementation during its creation)

All implementations of

java.lang.Runnable

All implementations of

javax.swing.Action

Interpreter (recognizeable by behavioral methods returning a structurally different instance/type of the given instance/type; note that parsing/formatting is not part of the pattern, determining the pattern and how to apply it is)

java.util.Pattern

java.text.Normalizer

All subclasses of

java.text.Format

All subclasses of

javax.el.ELResolver

Iterator (recognizeable by behavioral methods sequentially returning instances of a different type from a queue)

All implementations of

java.util.Iterator

(thus among others also

java.util.Scanner

!).

All implementations of

java.util.Enumeration

Mediator (recognizeable by behavioral methods taking an instance of different abstract/interface type (usually using the command pattern) which delegates/uses the given instance)

java.util.Timer

(all

scheduleXXX()

methods)

java.util.concurrent.Executor#execute()

java.util.concurrent.ExecutorService

(the

invokeXXX()

and

submit()

methods)

java.util.concurrent.ScheduledExecutorService

(all

scheduleXXX()

methods)

java.lang.reflect.Method#invoke()

Memento (recognizeable by behavioral methods which internally changes the state of the whole instance)

java.util.Date

(the setter methods do that,

Date

is internally represented by a

long

value)

All implementations of

java.io.Serializable

All implementations of

javax.faces.component.StateHolder

Observer (or Publish/Subscribe) (recognizeable by behavioral methods which invokes a method on an instance of another abstract/interface type, depending on own state)

java.util.Observer

java.util.Observable

(rarely used in real world though)

All implementations of

java.util.EventListener

(practically all over Swing thus)

javax.servlet.http.HttpSessionBindingListener

javax.servlet.http.HttpSessionAttributeListener

javax.faces.event.PhaseListener

State (recognizeable by behavioral methods which changes its behaviour depending on the instance's state which can be controlled externally)

javax.faces.lifecycle.LifeCycle#execute()

(controlled by

FacesServlet

, the behaviour is dependent on current phase (state) of JSF lifecycle)

Strategy (recognizeable by behavioral methods in an abstract/interface type which invokes a method in an implementation of a different abstract/interface type which has been passed-in as method argument into the strategy implementation)

java.util.Comparator#compare()

, executed by among others

Collections#sort()

javax.servlet.http.HttpServlet

, the

service()

and all

doXXX()

methods take

HttpServletRequest

and

HttpServletResponse

and the implementor has to process them (and not to get hold of them as instance variables!).

javax.servlet.Filter#doFilter()

Template method (recognizeable by behavioral methods which already have a "default" behaviour definied by an abstract type)

All non-abstract methods of

java.io.InputStream

java.io.OutputStream

java.io.Reader

and

java.io.Writer

.

All non-abstract methods of

java.util.AbstractList

java.util.AbstractSet

and

java.util.AbstractMap

javax.servlet.http.HttpServlet

, all the

doXXX()

methods by default sends a HTTP 405 "Method Not Allowed" error to the response. You're free to implement none or any of them.

Visitor (recognizeable by two different abstract/interface types which has methods definied which takes each the other abstract/interface type; the one actually calls the method of the other and the other executes the desired strategy on it)

javax.lang.model.element.AnnotationValue

and

AnnotationValueVisitor

javax.lang.model.element.Element

and

ElementVisitor

javax.lang.model.type.TypeMirror

and

TypeVisitor

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