Introduction to Programming

Convert to another collection type

The four static methods that convert one type of collection into another include:

• ArrayList<T> list(Enumeration<T> e)
• Enumeration<T> enumeration(Collection<T> c)
• Queue<T> asLifoQueue(Deque<T> deque)
• Set<E> newSetFromMap(Map<E,Boolean> map)

The interface java.util.Enumeration is a legacy interface that came with Java 1, along with the legacy classes java.util.Hashtable and java.util.Vector that use it. It is very similar to the Iterator interface. In fact, an Enumeration type object can be converted into an Iterator type by using the Enumeration.asIterator() method.

All these methods are rarely used in mainstream programming, so we are listing them here only for completeness.