ITEC 3030 - L7: Object Oriented Design Patterns III

Observer Pattern

Design pattern for notifying changes to observers.

Model-View-Controller (MVC)

Architectural pattern separating application logic from UI.

Pull Model

Each party retrieves information when interested.

Polling

Periodically requesting information from another component.

Coupling

Dependency between components; changes affect each other.

Push Model

Notifies interested parties when changes occur.

Subject Interface

Defines methods for registering and notifying observers.

Observer Interface

Defines method for updating observers with new data.

ConcreteSubject

Implements Subject; maintains observer list and state.

ConcreteObserver

Implements Observer; reacts to state changes.

Inversion of Control (IoC)

B calls A instead of A calling B.

Callback

Function passed as an argument to another function.

ArrayList

Dynamic array implementation in Java for storing elements.

Abstract Class

Class that cannot be instantiated; may contain abstract methods.

Constructor

Special method for initializing new class instances.

MVC Goals

Decouple UI from data and manage multiple views.

Strategy Pattern

Encapsulates algorithms for interchangeable use.

Model-View-Adapter (MVA)

Mediator pattern ensuring views interact only through controllers.

Event Subscription

Process where observers register to receive updates.

State Change Notification

Informing observers when the subject's state changes.

Redraw Method

Updates the visual representation of a window.

Observer Registration

Adding an observer to the subject's list.

Observer Removal

Removing an observer from the subject's list.

Notify Observers

Calls update method on all registered observers.

Set Value Method

Updates the subject's value and notifies observers.

Performance Problem

Issues arising from inefficient checking for changes.

Maintenance Problem

Challenges due to tight coupling of components.

Window Class

Represents a UI window that observes file changes.

FileSystem Object

Represents the underlying file system in the experiment.

User Input

Data entered by the user through the UI.

View Tier

Layer responsible for displaying data to users.

Logic Tier

Layer handling application logic and processing.

Storage Tier

Layer managing data storage and retrieval.

Observer Pattern Implementation

Model acts as Subject; views act as Observers.

Update Method

Method called to refresh observer state.

Observer Registration Method

Method for adding observers to the subject.

Observer Notification Method

Method for informing observers of state changes.

Concrete Observer Update

Updates the observer's state based on subject's value.

Observer Pattern Benefits

Decouples components, enhances flexibility and scalability.

Observer Pattern Drawbacks

Potential for memory leaks if observers are not removed.

Observer Pattern Use Cases

Used in event handling, data binding, and UI updates.

Observer Pattern Variants

Includes push and pull models for notifications.

Observer Pattern Examples

Common in GUI frameworks and real-time systems.