com.twelvemonkeys.util.FilterIterator Maven / Gradle / Ivy
/*
* Copyright (c) 2008, Harald Kuhr
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
*
* * Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* * Neither the name of the copyright holder nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
package com.twelvemonkeys.util;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* Wraps (decorates) an {@code Iterator} with extra functionality, to allow
* element filtering. Each
* element is filtered against the given {@code Filter}, and only elements
* that are {@code accept}ed are returned by the {@code next} method.
*
* The optional {@code remove} operation is implemented, but may throw
* {@code UnsupportedOperationException} if the underlying iterator does not
* support the remove operation.
*
*
* @see FilterIterator.Filter
*
* @author Harald Kuhr
* @author last modified by $Author: haku $
* @version $Id: //depot/branches/personal/haraldk/twelvemonkeys/release-2/twelvemonkeys-core/src/main/java/com/twelvemonkeys/util/FilterIterator.java#1 $
*/
public class FilterIterator implements Iterator {
protected final Filter filter;
protected final Iterator iterator;
private E next = null;
private E current = null;
/**
* Creates a {@code FilterIterator} that wraps the {@code Iterator}. Each
* element is filtered against the given {@code Filter}, and only elements
* that are {@code accept}ed are returned by the {@code next} method.
*
* @param pIterator the iterator to filter
* @param pFilter the filter
* @see FilterIterator.Filter
*/
public FilterIterator(final Iterator pIterator, final Filter pFilter) {
if (pIterator == null) {
throw new IllegalArgumentException("iterator == null");
}
if (pFilter == null) {
throw new IllegalArgumentException("filter == null");
}
iterator = pIterator;
filter = pFilter;
}
/**
* Returns {@code true} if the iteration has more elements. (In other
* words, returns {@code true} if {@code next} would return an element
* rather than throwing an exception.)
*
* @return {@code true} if the iterator has more elements.
* @see FilterIterator.Filter#accept
*/
public boolean hasNext() {
while (next == null && iterator.hasNext()) {
E element = iterator.next();
if (filter.accept(element)) {
next = element;
break;
}
}
return next != null;
}
/**
* Returns the next element in the iteration.
*
* @return the next element in the iteration.
* @see FilterIterator.Filter#accept
*/
public E next() {
if (hasNext()) {
current = next;
// Make sure we advance next time
next = null;
return current;
}
else {
throw new NoSuchElementException("Iteration has no more elements.");
}
}
/**
* Removes from the underlying collection the last element returned by the
* iterator (optional operation). This method can be called only once per
* call to {@code next}. The behavior of an iterator is unspecified if
* the underlying collection is modified while the iteration is in
* progress in any way other than by calling this method.
*/
public void remove() {
if (current != null) {
iterator.remove();
}
else {
throw new IllegalStateException("Iteration has no current element.");
}
}
/**
* Used to tests whether or not an element fulfills certain criteria, and
* hence should be accepted by the FilterIterator instance.
*/
public static interface Filter {
/**
* Tests whether or not the element fulfills certain criteria, and hence
* should be accepted.
*
* @param pElement the element to test
* @return {@code true} if the object is accepted, otherwise
* {@code false}
*/
public boolean accept(E pElement);
}
}