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    Head First Design Patterns
    Dedication
    A Note Regarding Supplemental Files
    Praise for Head First Design Patterns
    More Praise for Head First Design Patterns
    Praise for the Head First approach
    Authors/Developers of Head First Design Patterns
    Creators of the Head First series (and co-conspirators on this book)
    How to Use This Book: Intro
    1. Intro to Design Patterns: Welcome to Design Patterns
    2. The Observer Pattern: Keeping your Objects in the know
    The Weather Monitoring application overview
    Unpacking the WeatherData class
    What do we know so far?
    Taking a first, misguided SWAG at the Weather Station
    What’s wrong with our implementation?
    Meet the Observer Pattern
    Publishers + Subscribers = Observer Pattern
    A day in the life of the Observer Pattern
    Five minute drama: a subject for observation
    Two weeks later...
    The Observer Pattern defined
    The Observer Pattern defined: the class diagram
    The power of Loose Coupling
    Cubicle conversation
    Designing the Weather Station
    Implementing the Weather Station
    Implementing the Subject interface in WeatherData
    Now, let’s build those display elements
    Power up the Weather Station
    Using Java’s built-in Observer Pattern
    How Java’s built-in Observer Pattern works
    Reworking the Weather Station with the built-in support
    Running the new code
    The dark side of java.util.Observable
    Other places you’ll find the Observer Pattern in the JDK
    And the code...
    Tools for your Design Toolbox
    Exercise Solutions
    3. The Decorator Pattern: Decorating Objects
    4. The Factory Pattern: Baking with OO Goodness
    5. The Singleton Pattern: One of a Kind Objects
    6. The Command Pattern: Encapsulating Invocation
    7. The Adapter and Facade Patterns: Being Adaptive
    8. The Template Method Pattern: Encapsulating Algorithms
    9. The Iterator and Composite Patterns: Well-Managed Collections
    10. The State Pattern: The State of Things
    11. The Proxy Pattern: Controlling Object Access
    12. Compound Patterns: Patterns of Patterns
    13. Better Living with Patterns: Patterns in the Real World
    A. Appendix: Leftover Patterns
    B.
    C. Mighty Gumball
    Index
    About the Authors
    Colophon
    Copyright
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    Exercise Solutions

    Sharpen your pencil

    Based on our first implementation, which of the following apply? (Choose all that apply.)

    A.

    We are coding to concrete implementations, not interfaces.

    B.

    For every new display element we need to alter code.

    C.

    We have no way to add display elements at run time.

    D.

    The display elements don’t implement a common interface.

    E.

    We haven’t encapsulated what changes.

    F.

    We are violating encapsulation of the WeatherData class.

    Design Principle Challenge

    Note

    Design Principle

    Identify the aspects of your application that vary and separate them from what stays the same.

    __The thing that varies in the Observer Pattern_______

    __is the state of the Subject and the number and_____

    __types of Observers. With this pattern, you can______

      

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