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According to the Java API, Interface Enumeration<E> documentation [API 2011], Interface Enumeration<E> documentation,

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

As an example, an Enumeration is used in the following code to display the contents of a Vector.:

for (Enumeration e = vector.elements(); e.hasMoreElements();) {
  System.out.println(e.nextElement());
}

Unfortunately, a Vector and an Enumeration may not always work well together. In fact, the Java API [API 2011] recommends, "New implementations should consider using Iterator in preference to Enumeration." . Consequently, iterators rather than enumerators should be preferred when examining iterable collections.

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According to the Java API, Interface Iterator<E> documentation [API 2011], Interface Iterator<E> documentation,

Iterator takes the place of Enumeration in the Java collections framework. Iterators differ from enumerations in two ways:

• Iterators allow the caller to remove elements from the underlying collection during the iteration with well-defined semantics.
• Method names have been improved.

This compliant solution remedies the problem described in the noncompliant code example and demonstrates the advantages of using an Iterator over an Enumeration.:

class BankOperations {
  private static void removeAccounts(Vector v, String name) {
    Iterator i = v.iterator();
	 
    while (i.hasNext()) {
      String s = (String) i.next();
      if (s.equals(name)) {
        i.remove(); // Correctly removes all instances of the name Harry
      }
    }

    // Display current account holders
    System.out.println("The names are:");
    i = v.iterator();
    while (i.hasNext()) {
      System.out.println(i.next()); // Prints Dick, Tom only	 
    }
  }
	 
  public static void main(String args[]) {
    List list = new ArrayList(Arrays.asList(
      new String[] {"Dick", "Harry", "Harry", "Tom"}));
    Vector v = new Vector(list);
    remove(v, "Harry"); 
  }
}

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Using Enumeration when performing remove operations on a vector may cause unexpected program behavior.

Bibliography

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