JAVA EE: Layer Supertype Design Pattern

Thursday, 15 August 2013

Layer Supertype Design Pattern

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What is the Layer Supertype Pattern?

The Layer Supertype design pattern is a core member of the base patterns family in enterprise application architecture. Simply stated, a Layer Supertype is a type that acts as the supertype for all types in its layer.

In layered architectures, multiple classes living in the same architectural tier often require the exact same methods, properties, or utility logic. Instead of duplicating this code across every class, the Layer Supertype pattern pulls common behavior into a single, shared parent class or interface.

Real-World Example: StudentDAO & CustomerDAO

Consider an application with a data access layer containing classes like StudentDAO and CustomerDAO:

The Problem (Code Duplication): StudentDAO has a method to save student data, while CustomerDAO has a method to save customer data. However, both classes also contain an identical executeSQL() method to run queries and return results.
The Solution (Layer Supertype): We define a parent class named CommonDAO and place the shared executeSQL() method inside it.
Inheritance & Reuse: Both StudentDAO and CustomerDAO now extend CommonDAO. They inherit executeSQL() automatically without duplicating a single line of database execution code.

Key Advantages

Eliminates Code Duplication: Pulls identical behaviors scattered across the same layer into one centralized location.
Enhanced Reusability: Any new class added to the layer instantly gains access to established baseline functionality by extending the supertype.
Simplified Maintenance: Bug fixes or improvements made to the supertype automatically apply across all subclasses in that layer.