Observed design patterns in java source code.
#Factory javax.xml.parsers.DocumentBuilderFactory.newInstance() javax.xml.xpath.XPathFactory.newInstance() java.util.Calendar.getInstance()
#Singleton java.lang.Runtime.getRuntime() java.lang.System.getSecurityManager()
#Decorator Subclasses of java.io.InputStream, OutputStream, Reader and Writer. java.util.Collections.checked---(), synchronized---() and unmodifiable---().
#Chain of responsibility java.util.logging.Logger.log() javax.servlet.Filter.doFilter()