Software Design lesson final project.
An android e-commerce application prototype (without a database) that developed with Java.

• Singleton
• Proxy
• Observer
• Decorator
• Strategy

• Singleton: Only one user can use the application on the current device and a user has only one basket.
• Proxy: Only users who has seller license and have their account approved can sell.
• Observer: Users should be informed by the system when the prices in their basket change.
• Decorator: Users may want to receive from different communication channels (mail, sms, etc.) when their prices in their basket change.
• Strategy: Users can choose one of multiple payment methods (credit card, cash on delivery, etc.) to pay for the order, and change this selection at runtime (before completing the purchase).