Examples of Design Patterns within Java

• Some Creational patterns Examples
  • Factory method
    • java.util.Calendar#getInstance() & java.nio.charset.Charset#forName()
  • Prototype
    • java.lang.Object#clone()
  • Singleton
    • java.lang.Runtime#getRuntime() & java.lang.System#getSecurityManager()
• Some Structural patterns
  • Adapter
    • java.util.Arrays#asList() & javax.xml.bind.annotation.adapters.XmlAdapter#marshal() and #unmarshal()
  • Decorator
    • All subclasses of java.io.InputStream, OutputStream etc. & java.util.Collections : synchronizedXXX() and unmodifiableXXX() methods.
  • Flyweight
    • java.lang.Integer#valueOf(int) (also on other Wrapper classes)
• Behavioral patterns
• Chain of responsibility
  • javax.servlet.Filter#doFilter() & Exception Handling
• Command
  • java.lang.Runnable
• Iterator
  • All implementations of java.util.Iterator
• 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 others Collections#sort().
• Template method (recognizeable by behavioral methods which already have a "default" behaviour definied by an abstract type)
• All non-abstract methods of java.util.AbstractList, java.util.AbstractSet and java.util.AbstractMap.

References:

https://github.com/in28minutes/interview-guide