Design Pattern Used In JDK

Flyweight : use sharing to support a large number of objects that have part of their internal state in common where the other part of state can vary. Examples –

• java.lang.Integer#valueOf(int) (also on Boolean, Byte, Character, Short, Long, Float and Double)
• Java String creation.

Proxy : provide a placeholder for an object to control references to it. If you use spring framework, you should be very well acquainted with Proxy.

Used in jdk:

• Java RMI
• All libraries which use Java proxy , Reflection proxy and CGLIB proxy
• Spring AOP creates proxies for supplied objects

Decorator: add additional responsibilities dynamically to an object. Examples –

Used in jdk:

• All sub-classes 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
• Display tag custom tag library proved option to decorator for rendering of tables in JSP.
• Any client side JavaScript library which has render-er or parser like Yahoo UI datatable, JQuery grid


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