Design-patterns

Creational design patterns

1. Singleton Pattern
2. Builder Pattern
3. ProtoType Pattern
4. Factory Method pattern
5. Abstract Factory Pattern

3. Prototype pattern

3.1 Overview

• AVoids costly creation
• Avoids subclassing
• Typically doesn't use new
• Often utilizes an Interface
• Usually implemented with a Registry
• Example:
  • java.lang.Object#clone()

3.2 pitfalls

• Sometimes not clear when to use
• Used with other patterns
• SHallow copy only

4. Factory Method pattern

4.1 Overview

• Doesn't expose instantiation logic
• Defer to subclass
• Common interface
• Specified by architecture, implemented by user
• Example:
  • Calendar
  • ResourceBundle
  • NumberFormat

Design

Factory is responsible for lifecycle
Common Interface
Concrete Classes
Parameterized create method

4.2 pitfalls

• Complexity, need to write a lot of code
• Refactoring is not possible

5. Abstract Factory pattern

5.1 Overview

• Factory of Factories
• Factory of related objects
• Common interface
• Defer to subclass
• Example:
  • DocumentBuilder

Design

Group Factories together
Factory is responsible for lifecycle
Common Interface
Concrete Classes
Parameterized create method
Build using composition

5.2 pitfalls

• Complexity, need to write a lot of code
• Refactoring is not possible