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Design Pattern
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Structural Patterns are design
patterns, which describe the best
possible ways to combine the objects
and classes forming a larger complex
structure in an easy manner. It deals
with the objects delegating
responsibilities to other objects. It
is a simple way to design and realize
relationships between the
entities.
In this article, we are discussing
Decorator, Façade and Flyweight
Design Patterns.
I. Decorator Design Pattern
This section deeply discusses the
Decorator design pattern, a kind of
structural pattern.
In object-oriented programming, the
decorator pattern allows the
developers to add new behaviors to an
existing functionality of an object,
dynamically.
The decorator pattern can be used
whenever there is a need to add some
additional functionality to an object
or to the group of objects. It
provides a flexible alternative for
subclassing to extend the
functionality. This pattern is also
known as the “wrapper” design
pattern as it works by wrapping around
the original object to get a new “decorator”
object. Wrapping is typically achieved
by passing the original object as a
parameter to the
constructor of the decorator, and then
it is ready to implement the new
functionality.
Decorators are very much similar to
subclassing feature of an
object-oriented programming. The only
difference is that, Subclassing adds
behavior at compile time where as a
decoratorprovides a new behavior at
the runtime.
The UML diagram for this pattern in
our scenario looks something like
this:
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This
UML diagram illustrates that the
Decorators should be abstract classes
and the concrete implementation should
be derived from them according to the
requirement.
A decorator can be added or removed
from an object without realizing the
client about any changed occurred. It
is a good idea to use a Decorator in a
situation where you want to change the
behavior of an object repeatedly (by
adding and subtracting functionality)
during runtime.
This dynamic behavior modification
capability of the decorators are
useful for adapting objects to new
functionality without re-writing the
original object’s code.
The given design pattern shows the
implementation code of the decorated
class.In java, the code for a
decorator class would be something
like this:
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Nov 2007 | Java Jazz Up |37 |
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