Exploring Design Patterns in Java API

Every one reads about Design patterns,try some sample codes given on websites,blogs,ebooks etc. But all have a only one question in common : Find the flavours of that one question below: Can you give some real time example where design patterns are used? Can you tell where do we use these design pattern? What the use of design patterns in Programming? You can find an overview of a lot design patterns in Wikipedia. It also mentions which patterns are mentioned by GoF (Gang of Four). While I was reading for some good articles for Design patterns, I found one which was worth reading, it summarises as much as possible design pattern implementations found in both the Java SE and Java EE API's. I myself is not aware of all the below design patterns but can relate the ones I know. Have a look below. Creational patterns 1) Abstract Factory 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() 2) Builder 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() 3) Factory Method 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() 4) Prototype java.lang.Object#clone() (the class has to implement java.lang.Cloneable) 5) Singleton  java.lang.Runtime#getRuntime() java.awt.Desktop#getDesktop() Structural patterns 6) Adapter  java.io.InputStreamReader(InputStream) (returns a Reader) java.io.OutputStreamWriter(OutputStream) (returns a Writer) javax.xml.bind.annotation.adapters.XmlAdapter#marshal() and #unmarshal() 8) Composite 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, FloatBuffer and DoubleBuffer) java.awt.Container#add(Component) (practically all over Swing) 9) Decorator 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 10) Facade  javax.faces.context.FacesContext, it internally uses among others the abstract/interface types LifeCycle, ViewHandler, NavigationHandler and many more without that the end-user has to worry about it. javax.faces.context.ExternalContext, which internally uses ServletContext,HttpSession, HttpServletRequest, HttpServletResponse, etc. 11) Flyweight java.lang.Integer#valueOf(int) (also on Boolean, Byte, Character, Short, Long, Floatand Double) 12) Proxy java.lang.reflect.Proxy java.rmi.*, the whole API actually. Behavioral patterns 13) Chain of Responsibility  java.util.logging.Logger#log() javax.servlet.Filter#doFilter() 14) Command All implementations of java.lang.Runnable All implementations of javax.swing.Action 15) Interpreter java.util.Pattern java.text.Normalizer All subclasses of java.text.Format All subclasses of javax.el.ELResolver 16) Iterator All implementations of java.util.Iterator  java.util.Scanner All implementations of java.util.Enumeration 17) Mediator  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() 18) Memento java.util.Date All implementations of java.io.Serializable All implementations of javax.faces.component.StateHolder 19) Observer (or Publish/Subscribe)  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 20) State javax.faces.lifecycle.LifeCycle#execute() (controlled by FacesServlet, the behaviour is dependent on current phase (state) of JSF lifecycle) 21) Strategy java.util.Comparator#compare(), executed by among others Collections#sort(). javax.servlet.http.HttpServlet, the service() and all doXXX() methods takeHttpServletRequest and HttpServletResponse and the implementer has to process them. javax.servlet.Filter#doFilter() 22) Template method All non-abstract methods of java.io.InputStream, java.io.OutputStream, java.io.Readerand java.io.Writer. All non-abstract methods of java.util.AbstractList, java.util.AbstractSet andjava.util.AbstractMap. javax.servlet.http.HttpServlet, all the doXXX() methods by default sends a HTTP 405 "Method Not Allowed" error to the response. 23) Visitor javax.lang.model.element.AnnotationValue and AnnotationValueVisitor javax.lang.model.element.Element and ElementVisitor javax.lang.model.type.TypeMirror and TypeVisitor Reference of the Article: http://stackoverflow.com/questions/1673841/examples-of-gof-design-patterns