Adapter Design pattern - Class diagram

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Introduction

The Adapter Design Pattern is a structural design pattern that bridges two incompatible interfaces, allowing them to collaborate seamlessly. To understand how the pattern is modeled in software architecture, we look at its UML Class Diagrams. Depending on whether you use object composition or class inheritance, the pattern takes the form of an Object Adapter or a Class Adapter.

Key Participants in the Class Diagram

• Client: The class containing the business logic that invokes operations through the Target interface.
• Target Interface: Defines the domain-specific contract or method signatures that the Client expects to interact with (e.g., request()).
• Adaptee: The existing class or legacy/third-party component that contains useful functionality but provides an incompatible interface (e.g., specificRequest()).
• Adapter: The intermediary class that implements the Target interface and maps calls from the Client to the Adaptee.

Object Adapter vs. Class Adapter Diagram

1. Object Adapter (Composition)

In the Object Adapter design:

• The Adapter class implements the Target interface.
• The Adapter maintains an instance variable reference to the Adaptee (has-a relationship / composition).
• When request() is called, the Adapter delegates the call to adaptee.specificRequest().

2. Class Adapter (Inheritance)

In the Class Adapter design:

• The Adapter class implements the Target interface.
• The Adapter directly extends (subclasses) the Adaptee class (is-a relationship / inheritance).
• When request() is called, the Adapter calls the inherited method specificRequest() directly.

Structural Comparison

Feature	Object Adapter	Class Adapter
Relationship with Adaptee	Composition (Holds a reference)	Inheritance (Extends Adaptee)
Flexibility	High (Works with Adaptee and all its subclasses)	Rigid (Tied to a specific Adaptee class)
Java Support	Fully supported and preferred	Requires Target to be an interface due to single inheritance

Related Tutorials from Ram N Java

• Adapter Design Pattern: Sequence Diagram Explained
• Adapter Design Pattern Implementation: Class Adapter Example
• Adapter Design Pattern Implementation: Object Adapter Example
• Adapter Design Pattern: Introduction and Basics
• Adapter Design Pattern: Key Points You Need to Know

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Adapter Design pattern - Class diagram

See also:

Adapter Design pattern - Introduction

Adapter Design Pattern - Real Time Exmaple(Translator)

Adapter Design pattern - Real Time Example (Card Reader)

Adapter Design pattern - Real Time Example (Mobile Charger)

Adapter Design pattern - Real Time Example (Universal Adaptor)

Adapter Design pattern - Real Time Example [JDBC Driver]

Adapter Design Pattern - Sequence diagram

Adapter Design Pattern - Implementation [Language Translator]

Adapter Pattern - Implementation [Object Adapter]

Adapter Pattern - Implementation [Class Adapter]

Adapter Design Pattern - Implementation [Mobile Charger]

Adapter Design Pattern - Key Points

All Design Patterns Links