Collection<E> The root interface in the collection hierarchy
Comparator<T> A comparison function, which imposes a total ordering on some collection of objects. 
Deque<E> A linear collection that supports element insertion and removal at both ends. 
Enumeration<E> An object that implements the Enumeration interface generates a series of elements, one at a time. 
EventListener A tagging interface that all event listener interfaces must extend. 
Formattable The Formattable interface must be implemented by any class that needs to perform custom formatting using the 's' conversion specifier of Formatter
Iterator<E> An iterator over a collection. 
List<E> An ordered collection (also known as a sequence). 
ListIterator<E> An iterator for lists that allows the programmer to traverse the list in either direction, modify the list during iteration, and obtain the iterator's current position in the list. 
Map<K, V> An object that maps keys to values. 
Map.Entry<K, V> A map entry (key-value pair). 
NavigableMap<K, V> A SortedMap extended with navigation methods returning the closest matches for given search targets. 
NavigableSet<E> A SortedSet extended with navigation methods reporting closest matches for given search targets. 
Observer A class can implement the Observer interface when it wants to be informed of changes in observable objects. 
PrimitiveIterator<T, T_CONS> A base type for primitive specializations of Iterator
PrimitiveIterator.OfDouble An Iterator specialized for double values. 
PrimitiveIterator.OfInt An Iterator specialized for int values. 
PrimitiveIterator.OfLong An Iterator specialized for long values. 
Properties.XmlLoader Creates a dynamic dependency on XML support so that XML support can be excluded from the application binary without incurring link errors. 
Queue<E> A collection designed for holding elements prior to processing. 
RandomAccess Marker interface used by List implementations to indicate that they support fast (generally constant time) random access.