Head-First-Design-Patterns

6. Light Control Command

5 Battery Tracker Alexa

4 - 1. Cricket App (tradtional way)

Issue:

1. CricketData holds references to concrete display elements objects even tho it needs to call only the update methods of these objects.
2. currentScoreDisplay.update(runs, wickets, overs) violates one of the most important design principle "Program to interface, not implementations"

4 - 2, use Observer Pattern

3. Coffee Order System

2. Weather Data report

1. Duck