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