Enumeration : Java Glossary

2006-03-08 by Roedy Green ©1996-2009 Canadian Mind Products
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Enumeration

An Enumeration is the old-style interface for going through the elements of a some sort of collection (but not a Collection) one by one. You use the Enumeration object once, then discard it.

Sample Code	Implementing
Generics	Learning More
Enumeration vs Iterator	Links

Sample Code

You use it like this:

Generics

Enumeration has been updated to work with generics like this:

Enumeration vs Iterator

Enumeration was the forerunner of Iterator. Iterator was introduced in JDK 1.2. New classes use Iterator but the old timers still support Enumeration. You will see Enumerations in Hashtable. elements, Properties. element and Vector. elements.

If the class of interest supports both Iterator and Enumeration, use Iterator.

Enumeration vs Iterator
Enumeration	Iterator Equivalent	Notes
Enumeration	Iterator	The name of the interface the doles out the elements one by one.
Hashtable.elements Properties.propertyNames Vector.elements	Collection.iterator	Typical name of method that provides the Enumeration or Iterator.
Enumeration.hasMoreElements	Iterator.hasNext	Are there more elements to come?
Enumeration.nextElement	Iterator.next	next element
	java.lang.Iterable	Interface noting that this class is capable of emitting an Iterator with the iterator method.
		Works in a for:each statement. e.g. for ( String value : someCollection )

Implementing

Implementing an Enumeration is much simpler than you might suppose. Just look at the code for some of the existing Enumerations and Iterators.

Learning More

Sun’s Javadoc on the Enumeration class : available:

on the web at java.sun.com
in the current JDK 1.6.0_11 or in the old JDK 1.5.0_17 on your local Windows J: drive.

Sun’s Javadoc on the Iterator class : available:

on the web at java.sun.com
in the current JDK 1.6.0_11 or in the old JDK 1.5.0_17 on your local Windows J: drive.

Sun’s Javadoc on the Iterable class : available:

on the web at java.sun.com
in the current JDK 1.6.0_11 or in the old JDK 1.5.0_17 on your local Windows J: drive.

Hashtable
Iterator
Properties
Vector

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