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COP 3331 Object Oriented Analysis and Design Chapter 9 – Patterns

COP 3331 Object Oriented Analysis and Design Chapter 9 – Patterns. Jean Muhammad. Overview. State Design Pattern Factory Design Pattern. State Design Pattern. Category: Behavioral Design Pattern Intent: Allow an object to alter its behavior when its internal state changes.

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COP 3331 Object Oriented Analysis and Design Chapter 9 – Patterns

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  1. COP 3331 Object Oriented Analysis and DesignChapter 9 – Patterns Jean Muhammad Reference – Object Oriented Software Development Using Java - Jia

  2. Overview • State Design Pattern • Factory Design Pattern Reference – Object Oriented Software Development Using Java - Jia

  3. State Design Pattern • Category: Behavioral Design Pattern • Intent: Allow an object to alter its behavior when its internal state changes. • Also known as: Objects for states. • Applicability: Use this state when • an object’s behavior depends upon its state and it must change it’s behavior at run time, depending upon that state. • methods have large, multipart conditional statements that depend on the object’s state (ie switch statements). Reference – Object Oriented Software Development Using Java - Jia

  4. State Design Pattern • Participants in the State Design Pattern: • Context: Defines the current state by maintaining an instance of a ConcreteState. • State: Defines an interface for encapsulating the behavior associated with a particular state of the context. • ConcreteState: place where each class implements a behavior associated with a state of context. Reference – Object Oriented Software Development Using Java - Jia

  5. Context requested State handle state.handle() ConcreteStateA handle() ConcreteStateB handle() Reference – Object Oriented Software Development Using Java - Jia

  6. Factory Design Pattern • Category: Creational Design Pattern • Intent: To define an interface for creating an object but defer instantiation to the subclasses. • Also known as: Virtual constructor. • Applicability: Use this state when • a class cannot anticipate the class of objects it must create. • a class defers to it’s subclasses to specify the objects to create. Reference – Object Oriented Software Development Using Java - Jia

  7. Factory Design Pattern • Participants in the State Design Pattern: • Product: Defines the interface of the objects to be created. • ConcreteProduct: Implements the Product interface, and may provide default implementation. • Creator: Defines one or more factory method that create abstract products, that is, objects of type Product. • ConcreteCreator: Overrides the factory method to return an instance of a ConcreteProduct. The Factory design pattern involves a factory class whose sole responsibility is to create objects. Reference – Object Oriented Software Development Using Java - Jia

  8. Product Creator factoryMethod() anOperation() Product = factoryMethod() ConcreteCreator factoryMethod() ConcreteProduct Return new ConcreteProduct() Reference – Object Oriented Software Development Using Java - Jia

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