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package org.apache.commons.collections.iterators;

import java.util.Collection;
import java.util.Enumeration;
import java.util.Iterator;

/** 
 * Adapter to make {@link Enumeration Enumeration} instances appear
 * to be {@link Iterator Iterator} instances.
 *
 * @since Commons Collections 1.0
 * @version $Revision: 1.6 $ $Date: 2004/01/14 21:43:14 $
 * 
 * @author <a href="mailto:jstrachan@apache.org">James Strachan</a>
 * @author <a href="mailto:dlr@finemaltcoding.com">Daniel Rall</a>
 */
public class EnumerationIterator implements Iterator {
    
    /** The collection to remove elements from */
    private Collection collection;
    /** The enumeration being converted */
    private Enumeration enumeration;
    /** The last object retrieved */
    private Object last;
    
    // Constructors
    //-----------------------------------------------------------------------
    /**
     * Constructs a new <code>EnumerationIterator</code> that will not
     * function until {@link #setEnumeration(Enumeration)} is called.
     */
    public EnumerationIterator() {
        this(null, null);
    }

    /**
     * Constructs a new <code>EnumerationIterator</code> that provides
     * an iterator view of the given enumeration.
     *
     * @param enumeration  the enumeration to use
     */
    public EnumerationIterator(final Enumeration enumeration) {
        this(enumeration, null);
    }

    /**
     * Constructs a new <code>EnumerationIterator</code> that will remove
     * elements from the specified collection.
     *
     * @param enum  the enumeration to use
     * @param collection  the collection to remove elements form
     */
    public EnumerationIterator(final Enumeration enum, final Collection collection) {
        super();
        this.enumeration = enum;
        this.collection = collection;
        this.last = null;
    }

    // Iterator interface
    //-----------------------------------------------------------------------
    /**
     * Returns true if the underlying enumeration has more elements.
     *
     * @return true if the underlying enumeration has more elements
     * @throws NullPointerException  if the underlying enumeration is null
     */
    public boolean hasNext() {
        return enumeration.hasMoreElements();
    }

    /**
     * Returns the next object from the enumeration.
     *
     * @return the next object from the enumeration
     * @throws NullPointerException if the enumeration is null
     */
    public Object next() {
        last = enumeration.nextElement();
        return last;
    }

    /**
     * Removes the last retrieved element if a collection is attached.
     * <p>
     * Functions if an associated <code>Collection</code> is known.
     * If so, the first occurrence of the last returned object from this
     * iterator will be removed from the collection.
     *
     * @exception IllegalStateException <code>next()</code> not called.
     * @exception UnsupportedOperationException if no associated collection
     */
    public void remove() {
        if (collection != null) {
            if (last != null) {
                collection.remove(last);
            } else {
                throw new IllegalStateException("next() must have been called for remove() to function");
            }
        } else {
            throw new UnsupportedOperationException("No Collection associated with this Iterator");
        }
    }

    // Properties
    //-----------------------------------------------------------------------
    /**
     * Returns the underlying enumeration.
     *
     * @return the underlying enumeration
     */
    public Enumeration getEnumeration() {
        return enumeration;
    }

    /**
     * Sets the underlying enumeration.
     *
     * @param enumeration  the new underlying enumeration
     */
    public void setEnumeration(final Enumeration enumeration) {
        this.enumeration = enumeration;
    }
    
}
