We are advancing through our journey of building various real-wrold applications. We have explored the Command, Observer, and Strategy patterns in the previous units. In this unit, we will integrate all three behavioral patterns into different scenarios to solve real-world problems.

In this unit, we will use different combinations of behavioral patterns to solve real-world problems. Let's have a quick recap of what each pattern does:

• Command Pattern: Encapsulates a request as an object, allowing clients to parameterize and queue requests.
• Observer Pattern: Defines a one-to-many dependency between objects, ensuring that when one object changes state, all its dependents are notified and updated automatically.
• Strategy Pattern: Defines a family of algorithms, encapsulates each one and makes them interchangeable. Clients can choose the algorithm to use at runtime.

In this unit, we will apply different combinations of behavioral patterns to solve real-world problems. We will build the following applications:

1. We will build a chat application that uses the Command pattern to send messages and the Observer pattern to notify users when a new message is received in a chat application.
2. We will build a game application that uses the Strategy pattern for different attack strategies and the Command pattern to run battle for a game application.
3. We will build a weather monitoring application that uses the Observer pattern to notify users when the weather changes and the Command pattern to set the weather.
4. Finally, we will build a chat application and order management system that uses all three patterns together.