Enumeration (Java SE 15 & JDK 15) (original) (raw)

All Known Subinterfaces:

[NamingEnumeration](../../../java.naming/javax/naming/NamingEnumeration.html "interface in javax.naming")<T>

All Known Implementing Classes:

[StringTokenizer](StringTokenizer.html "class in java.util")

public interface Enumeration

An object that implements the Enumeration interface generates a series of elements, one at a time. Successive calls to thenextElement method return successive elements of the series.

For example, to print all elements of a Vector<E> v:

for (Enumeration e = v.elements(); e.hasMoreElements();) System.out.println(e.nextElement());

Methods are provided to enumerate through the elements of a vector, the keys of a hashtable, and the values in a hashtable. Enumerations are also used to specify the input streams to aSequenceInputStream.

API Note:

The functionality of this interface is duplicated by the Iterator interface. In addition, Iterator adds an optional remove operation, and has shorter method names. New implementations should consider usingIterator in preference to Enumeration. It is possible to adapt an Enumeration to an Iterator by using theasIterator() method.

Since:

1.0

See Also:

Iterator, SequenceInputStream, nextElement(), Hashtable, Hashtable.elements(), Hashtable.keys(), Vector, Vector.elements()

• Method Summary

• Method Details

  • hasMoreElements

  boolean hasMoreElements()
  Tests if this enumeration contains more elements.
  Returns:
  true if and only if this enumeration object contains at least one more element to provide;false otherwise.

  • nextElement

  E nextElement()
  Returns the next element of this enumeration if this enumeration object has at least one more element to provide.
  Returns:
  the next element of this enumeration.
  Throws:
  [NoSuchElementException](NoSuchElementException.html "class in java.util") - if no more elements exist.

  • asIterator

  Returns an Iterator that traverses the remaining elements covered by this enumeration. Traversal is undefined if any methods are called on this enumeration after the call to asIterator.
  API Note:
  This method is intended to help adapt code that producesEnumeration instances to code that consumes Iterator instances. For example, the JarFile.entries() method returns an Enumeration<JarEntry>. This can be turned into an Iterator, and then theforEachRemaining() method can be used:

       JarFile jarFile = ... ;  
       jarFile.entries().asIterator().forEachRemaining(entry -> { ... });  
       

  (Note that there is also a JarFile.stream() method that returns a Stream of entries, which may be more convenient in some cases.)
  Implementation Requirements:
  The default implementation returns an Iterator whosehasNext method calls this Enumeration'shasMoreElements method, whose next method calls this Enumeration's nextElement method, and whose remove method throwsUnsupportedOperationException.
  Returns:
  an Iterator representing the remaining elements of this Enumeration
  Since:
  9