1. Composite and Related Patterns Kirk Scott

2. The pitohui, a poisonous bird of New Guinea

3. This is an introductory unit. These are the units/chapters belonging to this section of the course: Unit 25, Composite, book chapter 5 Unit 26, Chain of Responsibility, book chapter 12 Unit 27, Interpreter, book chapter 25 Unit 28, Visitor, book chapter 29

4. What will be given next is an extremely brief overview of these topics. You will find that the composite design pattern has a lot in common with trees Chain of responsibility, interpreter, and visitor all follow naturally, because interesting examples of those patterns can be built on top of composites/trees

5. Composite Book definition: The intent of the Composite pattern is to let clients treat individual objects and compositions of objects uniformly Comment mode on: A composite can consist of one or more components Each component may be a single item or another composite

6. In the verbal description above you may recognize the elements of a definition of a tree-like structure It is reminiscent of directory structures which can contain individual files as well as other directories This pattern has a distinctive UML diagram. See the next overhead

8. Chain of Responsibility Book definition: The intent of the Chain of Responsibility pattern is to avoid coupling the sender of a request to its receiver, by giving more than one object a chance to handle the request. Comment mode on: If a set of objects is linked together, you may call a method on one. Potentially that one calls a method on the next in the chain, and so on down the line

9. Interpreter Book definition: The intent of the Interpreter pattern is to let you compose executable objects according to a set of composition rules that you define. Comment mode on: This directly parallels composite Interpreters interpret commands Commands can consist of single commands or collections (composites) of commands

10. Visitor Book definition: The intent of Visitor is to let you define a new operation for a hierarchy without changing the hierarchy classes. Comment mode on: The relationship with composite is that the hierarchy you define the operation for may be the component/leaf/composite hierarchy which generates a tree

11. In Summary and Mnemonic Devices: Composite: = Tree Chain of Responsibility: Think “Tree of Responsibility” Interpreter: Remember the analogy between directory structures and program structures (routines and subroutines) Visitor: Visiting the branches and leaves of trees…

12. The End