Java Design Patterns

4.

Behavioral Patterns

4.1.

Overview of Behavioral Patterns

4.1.1.

Focus on Object Interaction

4.1.2.

Responsibility Assignment Goals

4.1.3.

Algorithm and Communication Management

4.1.4.

Common Characteristics

4.1.5.

Comparison Framework

4.2.

Strategy Pattern

4.2.1.

Intent and Applicability

4.2.2.

Problem Context

4.2.3.

Solution Structure

4.2.3.1.

Strategy Interface

4.2.3.2.

ConcreteStrategy Classes

4.2.3.3.

4.2.4.

Implementation in Java

4.2.4.1.

Interface-based Strategies

4.2.4.2.

Composition Usage

4.2.4.3.

Lambda Expression Integration

4.2.4.4.

Functional Interface Application

4.2.5.

Common Use Cases

4.2.5.1.

Runtime Algorithm Selection

4.2.5.2.

Conditional Logic Elimination

4.2.5.3.

Payment Processing Systems

4.2.5.4.

Sorting Algorithm Selection

4.2.6.

Consequences and Trade-offs

4.2.6.1.

Increased Flexibility

4.2.6.2.

Strategy Awareness Requirement

4.2.6.3.

Object Proliferation

4.2.6.4.

Performance Considerations

4.2.7.

Modern Java Enhancements

4.3.

Observer Pattern

4.3.1.

Intent and Applicability

4.3.2.

Problem Context

4.3.3.

Solution Structure

4.3.3.1.

Subject Interface

4.3.3.2.

ConcreteSubject Class

4.3.3.3.

Observer Interface

4.3.3.4.

ConcreteObserver Classes

4.3.4.

Implementation in Java

4.3.4.1.

Custom Observer Implementation

4.3.4.2.

Event Listener Mechanisms

4.3.4.3.

Reactive Programming Integration

4.3.4.4.

Thread Safety Considerations

4.3.5.

Common Use Cases

4.3.5.1.

Event Notification Systems

4.3.5.2.

Model-View-Controller Architecture

4.3.5.3.

User Interface Updates

4.3.5.4.

Data Binding Systems

4.3.6.

Consequences and Trade-offs

4.3.6.1.

Loose Coupling Benefits

4.3.6.2.

Update Cascade Risks

4.3.6.3.

Memory Leak Potential

4.3.6.4.

Performance Implications

4.3.7.

Advanced Implementation Techniques

4.4.

Command Pattern

4.4.1.

Intent and Applicability

4.4.2.

Problem Context

4.4.3.

Solution Structure

4.4.3.1.

Command Interface

4.4.3.2.

ConcreteCommand Classes

4.4.3.3.

4.4.3.4.

4.4.3.5.

4.4.4.

Implementation in Java

4.4.4.1.

Action Encapsulation

4.4.4.2.

Command Queuing

4.4.4.3.

Command Logging

4.4.4.4.

Undo Operation Support

4.4.5.

Common Use Cases

4.4.5.1.

Undo and Redo Functionality

4.4.5.2.

Task Queue Implementation

4.4.5.3.

Macro Recording

4.4.5.4.

Remote Procedure Calls

4.4.6.

Consequences and Trade-offs

4.4.6.1.

Sender-Receiver Decoupling

4.4.6.2.

Command Composition

4.4.6.3.

Increased Class Count

4.4.6.4.

Memory Usage Considerations

4.4.7.

Advanced Command Techniques

4.5.

Template Method Pattern

4.5.1.

Intent and Applicability

4.5.2.

Problem Context

4.5.3.

Solution Structure

4.5.3.1.

AbstractClass with Template Method

4.5.3.2.

ConcreteClass Implementations

4.5.4.

Implementation in Java

4.5.4.1.

Abstract Class Design

4.5.4.2.

Final Template Methods

4.5.4.3.

Hook Method Implementation

4.5.4.4.

Primitive Operation Definition

4.5.5.

Common Use Cases

4.5.5.1.

Algorithm Skeleton Definition

4.5.5.2.

Framework Development

4.5.5.3.

Code Reuse Facilitation

4.5.5.4.

Invariant Behavior Enforcement

4.5.6.

Consequences and Trade-offs

4.5.6.1.

Inverted Control Structure

4.5.6.2.

Subclass Flexibility Limitations

4.5.6.3.

Code Reuse Benefits

4.5.6.4.

Maintenance Advantages

4.5.7.

Design Guidelines

4.6.

4.6.1.

Intent and Applicability

4.6.2.

Problem Context

4.6.3.

Solution Structure

4.6.3.1.

4.6.3.2.

State Interface

4.6.3.3.

ConcreteState Classes

4.6.4.

Implementation in Java

4.6.4.1.

State Transition Management

4.6.4.2.

Composition-based Design

4.6.4.3.

State Factory Implementation

4.6.5.

Common Use Cases

4.6.5.1.

Object Behavior Changes

4.6.5.2.

State Machine Implementation

4.6.5.3.

Conditional Logic Replacement

4.6.5.4.

Workflow Management

4.6.6.

Consequences and Trade-offs

4.6.6.1.

Localized State Behavior

4.6.6.2.

State Transition Clarity

4.6.6.3.

Increased Class Count

4.6.6.4.

Performance Considerations

4.6.7.

State Management Strategies

4.7.

Chain of Responsibility Pattern

4.7.1.

Intent and Applicability

4.7.2.

Problem Context

4.7.3.

Solution Structure

4.7.3.1.

Handler Interface

4.7.3.2.

ConcreteHandler Classes

4.7.3.3.

Client Implementation

4.7.4.

Implementation in Java

4.7.4.1.

Handler Chain Construction

4.7.4.2.

Request Processing Logic

4.7.4.3.

Chain Termination Strategies

4.7.5.

Common Use Cases

4.7.5.1.

Request Processing Pipelines

4.7.5.2.

Event Handling Systems

4.7.5.3.

Logging Framework Implementation

4.7.5.4.

Authorization Chains

4.7.6.

Consequences and Trade-offs

4.7.6.1.

Reduced Coupling

4.7.6.2.

Request Handling Uncertainty

4.7.6.3.

Chain Configuration Flexibility

4.7.6.4.

Performance Implications

4.7.7.

Chain Management Techniques

4.8.

Iterator Pattern

4.8.1.

Intent and Applicability

4.8.2.

Problem Context

4.8.3.

Solution Structure

4.8.3.1.

Iterator Interface

4.8.3.2.

ConcreteIterator Class

4.8.3.3.

Aggregate Interface

4.8.3.4.

ConcreteAggregate Class

4.8.4.

Implementation in Java

4.8.4.1.

Java Iterator Interface

4.8.4.2.

Iterable Interface Usage

4.8.4.3.

Enhanced For-Each Loop

4.8.4.4.

Stream API Integration

4.8.5.

Common Use Cases

4.8.5.1.

Collection Traversal

4.8.5.2.

Uniform Access Patterns

4.8.5.3.

Data Structure Abstraction

4.8.5.4.

Lazy Evaluation Implementation

4.8.6.

Consequences and Trade-offs

4.8.6.1.

Traversal Logic Encapsulation

4.8.6.2.

Multiple Iterator Support

4.8.6.3.

Memory Usage Considerations

4.8.6.4.

Thread Safety Challenges

4.8.7.

Advanced Iterator Techniques

4.9.

Mediator Pattern

4.9.1.

Intent and Applicability

4.9.2.

Problem Context

4.9.3.

Solution Structure

4.9.3.1.

Mediator Interface

4.9.3.2.

ConcreteMediator Class

4.9.3.3.

Colleague Classes

4.9.4.

Implementation in Java

4.9.4.1.

Centralized Communication Logic

4.9.4.2.

Colleague Registration

4.9.4.3.

Message Routing Strategies

4.9.5.

Common Use Cases

4.9.5.1.

GUI Component Coordination

4.9.5.2.

Object Interdependency Reduction

4.9.5.3.

Communication Hub Implementation

4.9.5.4.

Workflow Orchestration

4.9.6.

Consequences and Trade-offs

4.9.6.1.

Centralized Control Benefits

4.9.6.2.

Mediator Complexity Risk

4.9.6.3.

Loose Coupling Promotion

4.9.6.4.

Single Point of Failure

4.9.7.

Design Considerations

4.10.

Memento Pattern

4.10.1.

Intent and Applicability

4.10.2.

Problem Context

4.10.3.

Solution Structure

4.10.3.1.

4.10.3.2.

Originator Class

4.10.3.3.

Caretaker Class

4.10.4.

Implementation in Java

4.10.4.1.

State Capture Mechanisms

4.10.4.2.

State Restoration Logic

4.10.4.3.

Encapsulation Preservation

4.10.5.

Common Use Cases

4.10.5.1.

Undo and Redo Operations

4.10.5.2.

State Snapshot Creation

4.10.5.3.

Checkpoint Implementation

4.10.5.4.

Transaction Rollback

4.10.6.

Consequences and Trade-offs

4.10.6.1.

Encapsulation Preservation

4.10.6.2.

Memory Overhead Concerns

4.10.6.3.

Performance Implications

4.10.6.4.

State Management Complexity

4.10.7.

Implementation Strategies

4.11.

Visitor Pattern

4.11.1.

Intent and Applicability

4.11.2.

Problem Context

4.11.3.

Solution Structure

4.11.3.1.

Visitor Interface

4.11.3.2.

ConcreteVisitor Classes

4.11.3.3.

Element Interface

4.11.3.4.

ConcreteElement Classes

4.11.4.

Implementation in Java

4.11.4.1.

Double Dispatch Mechanism

4.11.4.2.

Accept Method Implementation

4.11.4.3.

Visitor Method Overloading

4.11.5.

Common Use Cases

4.11.5.1.

Operation Addition to Object Structures

4.11.5.2.

Compiler Design

4.11.5.3.

Abstract Syntax Tree Processing

4.11.5.4.

Report Generation

4.11.6.

Consequences and Trade-offs

4.11.6.1.

Easy Operation Addition

4.11.6.2.

Element Addition Difficulty

4.11.6.3.

Breaking Encapsulation Risk

4.11.6.4.

Performance Considerations

4.11.7.

Design Guidelines

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5. Advanced Topics and Best Practices