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?
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Even though I'm sort of a broken clock with this one, Java XML API uses Factory a lot. I mean just look at this:
Document doc = DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(source);
String title = XPathFactory.newInstance().newXPath().evaluate("//title", doc);
...and so on and so forth.
Additionally various Buffers (StringBuffer, ByteBuffer, StringBuilder) use Builder.
java.util.Collection#Iterator is a good example of a Factory Method. Depending on the concrete subclass of Collection you use, it will create an Iterator implementation. Because both the Factory superclass (Collection) and the Iterator created are interfaces, it is sometimes confused with AbstractFactory. Most of the examples for AbstractFactory in the the accepted answer (BalusC) are examples of Factory, a simplified version of Factory Method, which is not part of the original GoF patterns. In Facory the Factory class hierarchy is collapsed and the factory uses other means to choose the product to be returned.
An abstract factory has multiple factory methods, each creating a different product. The products produced by one factory are intended to be used together (your printer and cartridges better be from the same (abstract) factory). As mentioned in answers above the families of AWT GUI components, differing from platform to platform, are an example of this (although its implementation differs from the structure described in Gof).
The Abstract Factory pattern is used in various places.
E.g., DatagramSocketImplFactory
, PreferencesFactory
. There are many more---search the Javadoc for interfaces which have the word "Factory" in their name.
Also there are quite a few instances of the Factory pattern, too.
Observable
, Observer
)ContainerAdapter
, ComponentAdapter
, FocusAdapter
, KeyAdapter
, MouseAdapter
are not adapters; they are actually Null Objects. Poor naming choice by Sun.BufferedInputStream
can decorate other streams such as FilterInputStream
)java.lang.Runtime#getRuntime()
is SingletonButtonGroup
for Mediator patternAction
, AbstractAction
may be used for different visual representations to execute same code -> Command patternand many more I guess
RMI is based on Proxy.
Should be possible to cite one for most of the 23 patterns in GoF:
I can't think of examples in Java for 10 out of the 23, but I'll see if I can do better tomorrow. That's what edit is for.
clone()
method can be used for this purpose.Source: Stackoverflow.com