The Java Collections Framework (JCF)

JCF defines four basic interfaces and numerous implementations of these interfaces:

All of these classes and interfaces are contained in the java.util package.

Notice that all interfaces and implementations are parameterized by the type of objects they contain.

For example:

Collection<Integer> scores = new TreeSet<Integer>();
SortedSet<Date> appointments = new TreeSet<Date>();
Set<Employee> staff = new HashSet<Employee>();
List<City> itinerary = new ArrayList<City>();
Queue<Event> schedule = new LinkedList<Event>();

Collections

Collection<T> defines the basic interface that allows users to add and remove elements of type T:

public interface Collection<T> {
   // Basic Operations
   int size();
   boolean isEmpty();
   boolean contains(T element);
   boolean add(T element); // Optional
   boolean remove(T element); // Optional
   Iterator<T> iterator();

   // Bulk Operations
   boolean containsAll(Collection<T> c);
   boolean addAll(Collectio<T>n c); // Optional
   boolean removeAll(Collection<T> c); // Optional
   boolean retainAll(Collection<T> c); // Optional
   void clear();              // Optional   

   // Array Operations
   T[] toArray();
   T[] toArray(Object a[]);
  
   // Overrides
   boolean equals(Object o);
   int hashCode();
}

Note that Java does not provide an implementation of this interface. Instead, Java provides implementations of more specific interfaces. A direct implementation of Collection would be a multiset.