1 define one-many dependency between objects so that when one object changes state, all of its dependent objects are notified and updated autommatically.
a. chain of responsibilty
b. event notification
c. abstract factory
d. observer
2 ensure a class has only one instance and provide a global point of access to it?
a single class factory
b proxy
c. singleton
d. flyweight
which patterrn is used to?
