week-nine.md

decorator pattern

• a decorator class implements some interface
  • it is an [insert interface name here]
• BUT it also has an instance of that interface
• "decoratee" is the instance of the interface that the decorator class has
• if you extend the decorator class...
  • instances of this concrete class can make the instance in the decorator class immutable
  • IF you @Override all the methods that modify the decoratee
  • this way you can safely make an instance of the concrete decorator that has an immutable [insert interface name here]
• any subclasses the interface requires must also be decorated, both in the decorator class and any concrete classes that extend the decorator

decorator example (from Dr. Whittaker)

• CollectionDecorator
  • the decorator class itself
  • implements Collection
  • has an instance of Collection called decoratee
  • also has a subclass IteratorDecorator that implements Iterator and has an instance of Iterator
• UnmodifiableCollection
  • extends CollectionDecorator
  • overrides all of its methods
  • leaves methods that modify the collection unimplemented (i.e. they throw Unimplemented exceptions)
  • also has a subclass UnmodifiableIterator that extends IteratorDecorator
    • the iterator methods that modify the collection (remove, add, etc.) throw Unimplemented exceptions