Introduction to Design Patterns & The Strategy Pattern

Introduction to Design Patterns #

Definition of a design pattern.
Purpose and benefits of design patterns.
- Reusability
- Readability
- Modularity
- Scalability
Categories of design patterns:
- Creational
- Structural
- Behavioral

Dive into Behavioral Patterns #

Brief explanation of Behavioral patterns.
Emphasis on how they handle object collaboration and responsibilities.

Introduction to the Strategy Pattern #

Definition of the Strategy pattern.
Objective: Define a family of algorithms, encapsulate each one, and make them interchangeable.
Key components:
- Context
- Strategy
- ConcreteStrategy

Real-life analogy for Strategy Pattern #

Example: Different travel modes (walking, driving, flying) to reach a destination.

Code Examples #

Class diagram #

   Context
     |
 Strategy <--- ConcreteStrategy1
          <--- ConcreteStrategy2
          <--- ConcreteStrategy3

Basic implementation #

// Strategy
public interface TravelStrategy {
    String travel();
}

// ConcreteStrategies
public class WalkStrategy implements TravelStrategy {
    @Override
    public String travel() {
        return "Walking to destination";
    }
}

public class DriveStrategy implements TravelStrategy {
    @Override
    public String travel() {
        return "Driving to destination";
    }
}

public class FlyStrategy implements TravelStrategy {
    @Override
    public String travel() {
        return "Flying to destination";
    }
}

// Context
public class Traveler {
    private TravelStrategy strategy;

    public Traveler(TravelStrategy strategy) {
        this.strategy = strategy;
    }

    public void setStrategy(TravelStrategy strategy) {
        this.strategy = strategy;
    }

    public String travel() {
        return this.strategy.travel();
    }
}

Using the Strategy pattern #

// Client code
public class Main {
    public static void main(String[] args) {
        Traveler john = new Traveler(new WalkStrategy());
        System.out.println(john.travel());  // Output: Walking to destination

        john.setStrategy(new DriveStrategy());
        System.out.println(john.travel());  // Output: Driving to destination
    }
}

Advantages of Strategy Pattern #

Flexibility in swapping algorithms.
Decoupling of algorithm from the client that uses it.
Promotes Open/Closed principle.

Common Use Cases #

Different payment methods in e-commerce applications.
Different compression techniques for files.
Varying rendering techniques in graphics engines.

Conclusion #

The importance of understanding design patterns in software development.
Encourage readers to experiment with the Strategy pattern and explore other design patterns.