GoF Design Patterns in Java's core libraries
214113-May-2015
I am learning GoF Java Design Patterns and I want to see some real life examples of them. What are some good examples of these Design Patterns in Java's core libraries?
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Anonymous User
14-May-2015Creational patterns
Abstract factory (recognizeable by creational methods returning the factory itself which in turn can be used to create another 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 an implementation of an abstract/interface type)
java.util.Calendar#getInstance()
java.util.ResourceBundle#getBundle()
java.text.NumberFormat#getInstance()
java.nio.charset.Charset#forName()
java.net.URLStreamHandlerFactory#createURLStreamHandler(String) (Returns singleton object per protocol)
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)
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)
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 usesthem. The java.util.Collections#newSetFromMap() and singletonXXX() methodshowevercomes 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,ReaderandWriterhave 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 typesLifeCycle,ViewHandler,NavigationHandlerand many 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
java.lang.Integer#valueOf(int)(also onBoolean,Byte,Character,ShortandLong)Proxy
(recognizable 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.Proxyjava.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 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)
java.lang.Runnablejavax.swing.ActionInterpreter
(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.Patternjava.text.Normalizerjava.text.Formatjavax.el.ELResolverIterator
(recognizeable by behavioral methods sequentially returning instances of a different type from a queue)
java.util.Iterator(thus among others alsojava.util.Scanner!).java.util.EnumerationMediator
(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(theinvokeXXX()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 by alongvalue)java.io.Serializablejavax.faces.component.StateHolderObserver (or Publish/Subscribe)
(recognizeable by behavioral methods which invokes a method on an instance of another abstract/interface type, depending on own state)
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 byFacesServlet, 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, theservice()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)
java.io.InputStream,java.io.OutputStream,java.io.Readerandjava.io.Writer.java.util.AbstractList,java.util.AbstractSetandjava.util.AbstractMap.javax.servlet.http.HttpServlet, all thedoXXX()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)