Listing Vault SE322 · chapter 06 · Creational Design Patterns

Chapter 06 — Creational Design Patterns

GoF classification, the five creational patterns, and the question each one answers about what varies when an object is built.

06chapter
—lists
—total items
06

Creational Design Patterns

10 lists

GoF Classification 3 × 2

By purpose

  • Creational — how objects get created
  • Structural — how classes and objects are composed
  • Behavioral — how behavior and communication are distributed

By scope

  • Class — varies through inheritance
  • Object — varies through composition

A Pattern Entry Documents 6

  1. Intent
  2. Applicability
  3. Structure
  4. Participants
  5. Consequences
  6. Examples

The Five Creational Patterns 5

PatternScopeIntent
Factory MethodClassDefine a creation operation and let subclasses choose the concrete product
Abstract FactoryObjectCreate families of related products without naming concrete classes
BuilderObjectBuild a complex object step by step, separating construction from representation
PrototypeObjectCreate new objects by copying a configured prototype
SingletonObjectEnsure one instance with a well-known access point

Factory Method — Key Points 4

  1. The creator uses the product but delegates the new to an overridable factory method
  2. Removes direct construction from client policy
  3. Use when the product type varies through extension
  4. Cost: extra classes and one more level of indirection

Abstract Factory — Key Points 4

  1. Enforces compatibility within a product family
  2. Clients depend on abstract product and factory interfaces
  3. Adding a new family is easy — one new class
  4. Adding a new product kind changes the interface and every factory

Builder — Key Points 4

  1. Handles optional parameters, validation and multiple representations
  2. A director can encode a reusable construction sequence
  3. Avoids telescoping constructors, at the cost of ceremony
  4. Validation belongs in build() — the one point where the object is complete

Prototype — Key Points 4

  1. Use when construction is expensive or runtime types vary
  2. Deep versus shallow copying must be a deliberate decision
  3. Hazards: identity, shared references, mutable state
  4. A prototype registry lets clients ask for a copy by key

Singleton — Key Points 4

  1. Complications: concurrency, lifecycle, serialization, class loaders
  2. A naive lazy getInstance() is not thread-safe
  3. Fixes: eager static field, double-checked locking, or an enum
  4. Costs: global state, hidden dependencies, harder testing

Pattern Selection Guide 4

What variesPattern
Many kinds of one product, chosen by extensionFactory Method
Families of products that must stay consistentAbstract Factory
One product with many optional parts or representationsBuilder
Expensive or run-time-configured setup to reusePrototype
Singularity is a genuine invariantSingleton

Selection Ground Rules 3

  1. Start with a plain constructor; add a pattern when the construction decision itself changes
  2. Prefer the simplest mechanism that preserves the required flexibility
  3. Patterns combine — an Abstract Factory is often a Singleton whose methods are Factory Methods