Examples of gof design patterns (example of the design pattern mentioned by gof in Java)

References

Reference 1: http://stackoverflow.com/questions/1673841/examples-of-gof-design-patterns

Reference 2: http://en.wikipedia.org/wiki/Design_pattern_ (computer_science)

Reference 3: http://zh.wikipedia.org/wiki/%E8% AE %BE%E8% AE %A1%E6%A8%A1%E5%BC%8F_ (% E8 % AE % a1 % E7 % AE % 97% E6 % 9C % ba)

Body

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 patternsabstract 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(ALLgetXXX()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 onCharBuffer,ShortBuffer,IntBuffer,LongBuffer,FloatBufferAndDoubleBuffer)
• javax.swing.GroupLayout.Group#addComponent()
• All implementationsjava.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 onBoolean,Byte,Character,Short,Long,FloatAndDouble)
• 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 implementjava.lang.Cloneable)

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

• java.lang.Runtime#getRuntime()
• java.awt.Desktop#getDesktop()

Structural patternsadapter (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)(ReturnsReader)
• java.io.OutputStreamWriter(OutputStream)(ReturnsWriter)
• 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 wocould benew LinkedHashMap(LinkedHashSet<K>, List<V>)Which returns an unmodifiable linked map which doesn't clone the items, but uses them.java.util.Collections#newSetFromMap()AndsingletonXXX()Methods however comes close.

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

• java.util.Map#putAll(Map)
• java.util.List#addAll(Collection)
• java.util.Set#addAll(Collection)
• java.nio.ByteBuffer#put(ByteBuffer)(Also onCharBuffer,ShortBuffer,IntBuffer,LongBuffer,FloatBufferAndDoubleBuffer)
• java.awt.Container#add(Component)(Practically all over swing thus)

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

• All subclassesjava.io.InputStream,OutputStream,ReaderAndWriterHave a constructor taking an instance of same type.
• Almost all implementationsjava.util.List,SetAndMapHave a constructor taking an instance of same type.
• java.util.Collections,checkedXXX(),synchronizedXXX()AndunmodifiableXXX()Methods.
• javax.servlet.http.HttpServletRequestWrapperAndHttpServletResponseWrapper

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 TypesLifeCycle,ViewHandler,NavigationHandlerAnd more without that the enduser has to worry about it (which are however overrideable by injection ).
• javax.faces.context.ExternalContext, Which internally usesServletContext,HttpSession,HttpServletRequest,HttpServletResponse, Etc.

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

• java.lang.Integer#valueOf(int)(Also onBoolean,Byte,Character,Short,Long,FloatAndDouble)

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 patternschain of responsibility (recognizeable by behavioral methods which (indirectly) invokes the same method Inanother 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 implementationsjava.lang.Runnable
• All implementationsjavax.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 subclassesjava.text.Format
• All subclassesjavax.el.ELResolver

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

• All implementationsjava.util.Iterator(Thus among others alsojava.util.Scanner!).
• All implementationsjava.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(ALLscheduleXXX()Methods)
• java.util.concurrent.Executor#execute()
• java.util.concurrent.ExecutorService(invokeXXX()Andsubmit()Methods)
• java.util.concurrent.ScheduledExecutorService(ALLscheduleXXX()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,DateIs internally represented bylongValue)
• All implementationsjava.io.Serializable
• All implementationsjavax.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 implementationsjava.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()(ControlledFacesServlet, 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 othersCollections#sort().
• javax.servlet.http.HttpServlet,service()And alldoXXX()Methods TakeHttpServletRequestAndHttpServletResponseAnd 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 METHODSjava.io.InputStream,java.io.OutputStream,java.io.ReaderAndjava.io.Writer.
• All non-Abstract METHODSjava.util.AbstractList,java.util.AbstractSetAndjava.util.AbstractMap.
• javax.servlet.http.HttpServlet, AlldoXXX()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 theother abstract/interface type; the one actually callthe method of the other and the other executes the desired strategy on it)

• javax.lang.model.element.AnnotationValueAndAnnotationValueVisitor
• javax.lang.model.element.ElementAndElementVisitor
• javax.lang.model.type.TypeMirrorAndTypeVisitor