Design Patterns
Design patterns are reusable solutions to common software design problems.
There are three core problem areas in object-oriented design:
- Object creation
- Object structure / composition
- Object behavior / interaction
That’s why we have:
- Creational Patterns
- Structural Patterns
- Behavioral Patterns
Design patterns are grouped / categorized based on what problem they primarily solve in software design.
1️⃣ Creational Patterns:
Who creates the object, when, and how?
Directly creating objects using new:
- Couples code tightly
- Makes changes difficult
- Makes testing harder
Creational patterns:
- Control object creation
- Hide creation logic
- Improve flexibility
Examples:
- Singleton
- Factory
- Abstract Factory
- Builder
- Prototype
2️⃣ Structural Patterns
👉 “How objects are connected or composed”
As systems grow:
- Classes increase
- Dependencies become complex
- Code becomes hard to manage
Structural patterns:
- Define relationships between classes
- Simplify object composition
- Improve readability and reuse
Examples:
- Adapter
- Decorator
- Facade
- Proxy
- Composite
3️⃣ Behavioral Patterns
👉 “How objects communicate and behave”
In real applications:
- Many objects talk to each other
- Logic gets scattered
- Changes become risky
Behavioral patterns:
- Define clear communication rules
- Separate responsibilities
- Reduce tight coupling between behaviors
Examples:
- Strategy
- Observer
- Command
- Template Method
- State
- Chain of Responsibility