Prototype Pattern

1
Prototype Pattern
2
Creational Pattern

• Specify the kinds of objects to create using a
  prototypical instance, and create new objects by
  copy this prototype.

3
Problem
Problem The GraphicTool class
belongs to the framework, while the graphical
classes are application-specific, so the
GraphicTool class doesn't know how to create
graphical objects and then operate on them.
4
Solution One
This method will produce many subclasses that are
different only in the kind of music objects they
instantiated.
5
Solution Two
6
Structure

• Participants
• Prototype(Graphic)
• declares an interface for cloning itself.
• ConcretePrototype
• (Staff,WholeNote,
• HalfNote)
• implements an operation for cloning itself.
• Client(GraphicalTool)
• - creates a new object by asking a prototype to
  clone itself.

7
Applicability

• The prototype pattern is used when a system
  should be independent of how its products are
  created, composed, and represented and
• when the classes to instantiate are specified at
  run-time for example, the dynamic loading
• to avoid building a class hierarchy of factories
  that parallels the class hierarchy of products
  or 
• when instances of a class can have one of only a
  few different combinations of state

8
Consequences

1. Isolating concrete product classes from the
   client.
2. Dynamically adding and removing products at
   run-time.
3. Specifying new objects by varying values.
4. Specifying new objects by varying structure.
5. Reducing the need for sub-classing.
6. Configuring an application with classes
   dynamically.
7. Main liability Clone() needed.

9
Implementation

1. Using a prototype manager.
2. Implementing the Clone operation.
3. Initializing clones.

10
Questions?