home | O'Reilly's CD bookshelfs | FreeBSD | Linux | Cisco | Cisco Exam    

Java Fundamental Classes Reference

Previous Chapter 17
The java.util Package
Next
 

Enumeration

Name

Enumeration

Synopsis

Interface Name:

java.util.Enumeration

Super-interface:

None

Immediate Sub-interfaces:

None

Implemented By:

java.util.StringTokenizer

Availability:

JDK 1.0 or later

Description

An object that implements the Enumeration interface provides a way to access a set of objects sequentially. The Enumeration object hides the actual organization of the set of objects from the code that is using it. An Enumeration can iterate through, or enumerate, its set of objects one at a time. A specific implementation of the interface controls the order in which the objects are presented.

The following is an example of how an Enumeration is used. The example shows a method for printing the values in an Enumeration:

void printAll(Enumeration e) {
    while ( e.hasMoreElements() ) {
        System.out.println(e.nextElement());
    }
}

Note that an Enumeration can be used only once: it iterates through its collection of objects in one direction and cannot be reset or rewound.

Normally, an Enumeration is not instantiated directly, but instead returned by a method that needs to enumerate a set of values. For example, the elements() method of the Vector class returns an Enumeration of the elements in the Vector. By the same token, the elements() and keys() methods of the Hashtable class return Enumeration objects for the keys and values in the Hashtable.

Interface Declaration

public abstract interface java.util.Enumeration {
  // Methods
  public abstract boolean hasMoreElements();
  public abstract Object nextElement() throws NoSuchElementException;
}

Methods

hasMoreElements

public abstract boolean hasMoreElements()

Returns

true if the there are more objects to retrieve; false otherwise.

Description

This method returns true if the nextElement() method of this Enumeration returns an object the next time it is called.

nextElement

public abstract Object nextElement()

Returns

The next object in this Enumeration.

Throws

NoSuchElementException

If there are no more objects to return.

Description

This method returns the next object in the set of objects encapsulated by this Enumeration.

See Also

Hashtable, StringTokenizer, Vector


Previous Home Next
EmptyStackException Book Index EventListener

Java in a Nutshell Java Language Reference Java AWT Java Fundamental Classes Exploring Java










??????????????@Mail.ru