Design Pattern

which misses definitions for one or more methods. Thus it
restricts the creation of an object of that class. You must first create a subclass and provide definitions for the abstract methods. Unlike interfaces, abstract classes may implement some of the methods. Though you can’t instantiate an abstract class, you can invoke its static methods. Abstract classes form an interesting and useful middle ground between interfaces and classes.

3 Delegation

The Delegation and Interface patterns are often used together. Delegation is used to avoid Inheritance. Delegation is a way of extending and reusing a class by writing another class with additional functionality that uses instances of the original class to provide the original functionality.

4 Marker Interface

The Marker Interface pattern uses interfaces declaring no
methods or variables to indicate semantic attributes of a
class. It works particularly well with utility classes that
determine something about objects without assuming that
they are an instance of any particular class.

5 Immutable

The Immutable pattern reduces the overhead of concurrent
access to an object and increases the robustness of objects that share references to the same object. It accomplishes this by not allowing an object’s state information to change after it is constructed. The Immutable pattern also avoids the need to synchronize multiple threads of execution that share an object.

6 Single Threaded Execution

The Single Threaded Execution pattern is the pattern most
frequently used to coordinate access by multiple threads to a shared object. The Immutable object pattern can be used to avoid the need for the Single Threaded Execution pattern or any other kind of access coordination.

7 Proxy

The Proxy pattern forces method calls to an object to occur indirectly through a proxy object that acts as a surrogate for the other object, delegating method calls to that object. Classes for proxy objects are declared in a way that usually eliminates client object’s awareness that they are dealing with a proxy. Proxy is a very general pattern that occurs in many other patterns, but never by itself in its pure form.


July 2007 | Java Jazz Up |30
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