Command Pattern

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Command Pattern

• Chihung Liao
• Cynthia Jiang

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Order Execute()
Waiter
Hamburger Execute()
Hot Dogs Execute()
Fries Execute()
Cook Make Food()
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Order Execute()
Abstract command (superclass)
Hamburger Execute()
Hot Dog Execute()
Fries Execute()
Concrete command (subclass)
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Command Execute()
Client
Invoker
Receiver Action()
ConcreteCommand Execute() State
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Flexibility and Extensibility

• Encapsulate a request as an object
• Compare to C function pointer
• Decouple the client and receiver by the invoker
  who ONLY invoke an operation
• Any request can be cancelled or added in form of
  stack
• Request to be executed can be stored as a queue

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Translate into JAVA 1

• Interface Command an interface for executing an
  operation
• (it could also be an abstract class, refer to
  the sample codes comment)
• Class Client creates a ConcreteCommand object
  and set its receiver
• Class Receiver who actually DOES things

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Translate into JAVA 2

• Class Invoker ask Command to carry out an
  execution, an agent between ConcreteCommand and
  Client
• Class ConcreteCommand implements Command MUST
  have the method in Interface Command

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QUESTIONS