📝 Week 4 Exercises

These exercises will help you apply design patterns in real code.

Focus on writing clean, readable, and well-structured solutions.

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✅ Exercise 1 – Singleton Pattern

Create a ConfigurationManager class that:

• Stores application configuration (e.g., appName, version)
• Can only have one instance
• Provides a getInstance() method

Requirements

• Constructor must be private
• Provide getters for configuration values
• Demonstrate usage in a main() method

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✅ Exercise 2 – Factory Pattern

Create a ShapeFactory that returns different shapes.

Step 1 – Create Interface

public interface Shape {
    void draw();
}

Step 2 – Implement Shapes

• Circle
• Rectangle
• Triangle

Step 3 – Create Factory

ShapeFactory.createShape(String type)

Step 4 – Test It

Create shapes using the factory and call draw().

✅ Goal: Client code should not use new Circle() directly.

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✅ Exercise 3 – Builder Pattern

Create a Product class using the Builder pattern.

Fields:

• name (required)
• price (required)
• description (optional)
• category (optional)

Requirements

• Use static inner Builder class
• Implement method chaining
• Demonstrate object creation using builder

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✅ Exercise 4 – Strategy Pattern

Build a discount system using Strategy pattern.

Step 1 – Create Interface

public interface DiscountStrategy {
    double applyDiscount(double amount);
}

Step 2 – Implement Strategies

• NoDiscount
• SeasonalDiscount (10%)
• PremiumCustomerDiscount (20%)

Step 3 – Create Context Class

ShoppingCart that accepts a DiscountStrategy.

Step 4 – Test

Apply different discount strategies dynamically.

✅ Goal: Avoid if-else chains.

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✅ Exercise 5 – DTO Pattern

Create:

• User entity class
• UserDTO class

Convert a User object into UserDTO.

Question

Why should password NOT be included in DTO?

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✅ Exercise 6 – Layered Architecture Refactor

Take your previous mini project and restructure it into:

controller
service
repository
model

Requirements

• Controller handles user input
• Service contains business logic
• Repository stores data (can use ArrayList instead of database)
• No layer should directly skip another layer

✅ Goal: Clear separation of responsibilities

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⭐ Bonus Challenge

Refactor your Layered Architecture project to:

• Use Factory for object creation
• Use Strategy for payment or discount logic
• Use DTO for data transfer

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✅ Submission Guidelines

• Follow proper package structure
• Use meaningful class names
• Add comments explaining pattern usage
• Keep methods small and focused

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💡 Reminder

Do not use patterns unnecessarily.

Ask yourself:

• Does this solve a real problem?
• Does this improve readability?
• Does this reduce coupling?

Clean code is the ultimate goal.