Design Pattern with Java IV Lecture 12-14 State Design Pattern and - - PowerPoint PPT Presentation

Design Pattern with Java IV

Lecture 12-14 State Design Pattern and Application to Mutable Linear Recursive Structure Framework

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State Pattern and Dynamic Reclassification

• Object, an instance of container structures

– can store, retrieve, and remove data

• A mutable container structure is a system that may

change its state.

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Dynamic Reclassification

• For each distinct state, the algorithms to

implement the methods differ.

• For example, retrieve method

– empty state -it simply returns null – non-empty state- it is more complicated

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UML Class Diagram for the State Design Pattern

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Mutable Linear Recursive Structure

• A mutable linear recursive structure (LRStruct)

can be in the empty state or in a non-empty state.

– empty, it contains no object – Non-empty, it contains an object called first, and a LRStruct object called rest.

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UML class diagram of the LRStruct

The intrinsic structural behavior of an LRStruct.

• The public constructor:

– LRStruct()

• and the methods:

– insertFront(...) – removeFront(...) – getFirst() – setFirst(...) – getRest() – setRest(...),

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The Extrinsic behaviors

• The method,

– Object execute(IAlgo algo, Object... inp),

is called the extensibility "hook".

• It allows the client to add an open-ended

number of new application-dependent behaviors to the data structure LRStruct,

– Computing its length – Merging one LRStruct with another

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Adding a new operation on an LRStruct

• The client writes appropriate concrete classes that

implements IAlgo . For example,

• With some concrete code for emptyCase(...) and some

concrete code for nonEmptyCase(...

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Client Code

• To perform an algorithm on an LRStruct , the

client must "ask" the LRStruct to "execute" the algorithm

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IMPLEMENTATION OF LINEAR RECURSIVE STRUCTURE FRAMEWORK

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UML class diagram of the LRStruct

The Structure

• LRStruct is the invariant part of the system. It

remains the same for all applications using LRStruct.

• The variant part of the system is the behaviors

that are abstractly encapsulated in an interface called IAlgo.

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LRStruct.java

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The States

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Example: Series of object diagrams

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The Visitor

• Algorithms on LRStruct are written as IAlgo

visitors

• The following slides show an algorithm to

remove the last element from an LRStruct.

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