Examples of GoF Design Patterns in Java's core libraries
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?
Design Patterns
Java
java-api
loops
- asked 9 years ago
- B Butts
1Answer
Creational patterns
Abstract factory (recognizeable by creational methods returning the factory itself which in turn can be used to create another abstract/interface type)
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 onCharBuffer
,ShortBuffer
,IntBuffer
,LongBuffer
,FloatBuffer
andDoubleBuffer
)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)
java.util.Arrays#asList()
java.io.InputStreamReader(InputStream)
(returns aReader
)java.io.OutputStreamWriter(OutputStream)
(returns aWriter
)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 usesthem. Thejava.util.Collections#newSetFromMap()
andsingletonXXX()
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
andWriter
have a constructor taking an instance of same type. java.util.Collections
, thecheckedXXX()
,synchronizedXXX()
andunmodifiableXXX()
methods.javax.servlet.http.HttpServletRequestWrapper
andHttpServletResponseWrapper
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
,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 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
andBigDecimal
)
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 inanother implementation of same 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 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 alsojava.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
(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,Date
is internally represented by along
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 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 takeHttpServletRequest
andHttpServletResponse
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
andjava.io.Writer
. - All non-abstract methods of
java.util.AbstractList
,java.util.AbstractSet
andjava.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)
javax.lang.model.element.AnnotationValue
andAnnotationValueVisitor
javax.lang.model.element.Element
andElementVisitor
javax.lang.model.type.TypeMirror
andTypeVisitor
java.nio.file.FileVisitor
andSimpleFileVisitor
- answered 8 years ago
- Gul Hafiz
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