A ListIterator
is equivalent to the List
interface. To demonstrate this, I'm writing a IteratorList
class which implements the List
interface over an underlying ListIterator
; it's actually quite simple. More fun with iterators! Here it is (note, not tested—I just wanted to sketch it out to see what it'd look like):
/* * IteratorList.java * Copyright 2003 (C) B. K. Oxley (binkley) * <binkley@alumni.rice.edu> * * This library is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public License * as published by the Free Software Foundation; either version 2.1 of * the License, or (at your option) any later version. * * This library is distributed in the hope that it will be useful, but * WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with this library; if not, write to the Free Software * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 * USA * * Created on June 4, 2003. */ package hm.binkley.util; import java.lang.reflect.Array; import java.util.AbstractList; import java.util.Iterator; import java.util.List; import java.util.ListIterator; /** * <code>IteratorList</code> implements <code>List</code> from an * underlying <code>ListIterator</code>. * * @author <a href="mailto:binkley@alumni.rice.edu">B. K. Oxley (binkley)</a> * @version 1.0 */ public class IteratorList extends AbstractList { /** The underlying list iterator. */ private final ListIterator it; /** * Constructs a <code>IteratorList</code> code from an underyling * <code>ListIterator</code> object. * * @param it the list iterator */ public IteratorList(ListIterator it) { this.it = it; } /** * Resets the underlying list iterator back to its starting state. */ private void reset() { while (it.hasPrevious()) it.previous(); } /** * Positions the underlying iterator before <var>index</var>. The * caller needs to then call {@link #next()} as required. * * @param index the index * @throws IndexOutOfBoundsException if <var>index</var> is out of * range */ private void scrollTo(int index) { if (index < 0) throw new IndexOutOfBoundsException(); // Ensure we call one extra next for the index itself while (index-- > 0) if (it.hasNext()) it.next(); else throw new IndexOutOfBoundsException(); } /** {@inheritDoc} */ public int size() { int n = 0; for ( ; it.hasNext(); ++n) it.next(); reset(); return n; } /** {@inheritDoc} */ public Object get(int index) { try { scrollTo(index); if (it.hasNext()) return it.next(); else throw new IndexOutOfBoundsException(); } finally { reset(); } } /** {@inheritDoc} */ public Object set(int index, Object element) { try { scrollTo(index); if (it.hasNext()) { Object old = it.next(); it.set(element); return old; } else throw new IndexOutOfBoundsException(); } finally { reset(); } } /** {@inheritDoc} */ public void add(int index, Object element) { try { scrollTo(index); if (it.hasNext()) { it.next(); it.add(element); } else throw new IndexOutOfBoundsException(); } finally { reset(); } } /** {@inheritDoc} */ public Object remove(int index) { try { scrollTo(index); if (it.hasNext()) { Object old = it.next(); it.remove(); return old; } else throw new IndexOutOfBoundsException(); } finally { reset(); } } }
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