Java设计模式之装饰者模式

DECORATOR （Object Structural）?
Purpose?
??? Allows for the dynamic wrapping of objects in order to modify?
their existing responsibilities and behaviors.?
Use When?
??? 1 Object responsibilities and behaviors should be dynamically?
?????? modifiable.?
??? 2 Concrete implementations should be decoupled from?
????? responsibilities and behaviors.?
??? 3 Subclassing to achieve modification is impractical or impossible.?
??? 4 Specific functionality should not reside high in the object hierarchy.?
??? 5 A lot of little objects surrounding a concrete implementation is?
????? acceptable.?
Example?
??? Many businesses set up their mail systems to take advantage of?
decorators. When messages are sent from someone in the company?
to an external address the mail server decorates the original?
message with copyright and confidentiality information. As long?
as the message remains internal the information is not attached.?
This decoration allows the message itself to remain unchanged?
until a runtime decision is made to wrap the message with?
additional information.?