JDK中有关23个经典设计模式的示例

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()

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, FloatBufferand 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, 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 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()

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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. Thejava.util.Collections#newSetFromMap()and singletonXXX()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 on CharBuffer, ShortBuffer, IntBuffer, LongBuffer,FloatBufferand DoubleBuffer)
• java.awt.Container#add(Component)(practically all over Swing thus)

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

• All subclasses of java.io.InputStream, OutputStream, Readerand Writerhave a constructor taking an instance of same type.
• Almost all implementations of java.util.List, Setand Maphave a constructor taking an instance of same type.
• java.util.Collections, the checkedXXX(), synchronizedXXX()and unmodifiableXXX()methods.
• javax.servlet.http.HttpServletRequestWrapperand HttpServletResponseWrapper

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

• javax.faces.webapp.FacesServlet, it internally uses among others the abstract/interface typesServletContext, LifeCycle, ViewHandler, NavigationHandlerand many more without that the enduser has to worry about it (which are however overrideable by injection).

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, Floatand 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.}}

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Behavioral patterns

Chain 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 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)}}

• All implementations of java.util.Iterator
• 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 HttpServletRequestand 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.Readerandjava.io.Writer.
• All non-abstract methods of java.util.AbstractList, java.util.AbstractSetandjava.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 otherabstract/interface type; the one actually calls the method of the other and the other executes the desired strategy on it)}}

• javax.lang.model.element.AnnotationValueand AnnotationValueVisitor
• javax.lang.model.element.Elementand ElementVisitor
• javax.lang.model.type.TypeMirrorand TypeVisitor