Using Collection Classes

• Collections hold only Objects, but primitives can be autoboxed.
• Iterate with the enhanced for, or with an Iterator via hasNext() & next().
• hasNext() determines if more elements exist; the Iterator does NOT move.
• next() returns the next element AND moves the Iterator forward.
• To work correctly, a Map's keys must override equals() and hashCode().
• Queues use offer() to add an element, poll() to remove the head of the queue, and peek() to look at the head of a queue.
• As of Java 6 TreeSets and TreeMaps have new navigation methods like floor() and higher().
• You can create/extend "backed" sub-copies of TreeSets and TreeMaps.