JDK源码中用到的设计模式

2019-05-25 本文已影响0人 huapro

Creational patterns

Abstract factory ^{_{(recognizeable by creational methods returning an abstract/interface type)}}

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)}}

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)}}

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 , Reader and Writer have a constructor taking an instance of same type.
Almost all implementations of java.util.List , Set and Map 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.webapp.FacesServlet , it internally uses among others the abstract/interface types ServletContext , LifeCycle , ViewHandler , NavigationHandler and 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 , Float and Double )

Proxy ^{_{(recognizeable by creational methods which returns an implementation of given abstract/interface type which in turn delegates/uses adifferent 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 ofsame abstract/interface type in a queue)}}

Command ^{_{(recognizeable by behavioral methods in an abstract/interface type which invokes a method in an implementation of a differentabstract/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)}}

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 anotherabstract/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 differentabstract/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)}}

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