rangeiteratoradapter.java

jsr170接口的java实现。是个apache的开源项目。

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.jackrabbit.commons.iterator;

import java.util.Collection;
import java.util.Iterator;
import java.util.NoSuchElementException;

import javax.jcr.RangeIterator;

/**
 * Adapter for turning normal {@link Iterator}s into {@link RangeIterator}s.
 * This helper class is used by the adapter classes in this package to
 * implement the JCR iterator interfaces on top of normal Java iterators.
 */
public class RangeIteratorAdapter implements RangeIterator {

	/**
	 * The adapted iterator instance.
	 */
	private final Iterator iterator;

	/**
	 * Number of elements in the adapted iterator, or -1 if unknown.
	 */
	private long size;

	/**
	 * Current position of the iterator.
	 */
	private long position;

	/**
	 * Creates an adapter for the given iterator of the given size.
	 *
	 * @param iterator adapted iterator
	 * @param size size of the iterator, or -1 if unknown
	 */
	public RangeIteratorAdapter(Iterator iterator, long size) {
		this.iterator = iterator;
		this.size = size;
		this.position = 0;
	}

	/**
	 * Creates an adapter for the given iterator of unknown size.
	 *
	 * @param iterator adapted iterator
	 */
	public RangeIteratorAdapter(Iterator iterator) {
		this(iterator, -1);
	}

	/**
	 * Creates a {@link RangeIterator} for the given collection.
	 *
	 * @param collection the collection to iterate
	 */
	public RangeIteratorAdapter(Collection collection) {
		this(collection.iterator(), collection.size());
	}

	//-------------------------------------------------------< RangeIterator >

	/**
	 * Returns the current position of the iterator.
	 *
	 * @return iterator position
	 */
	public long getPosition() {
		return position;
	}

	/**
	 * Returns the size of the iterator.
	 *
	 * @return iterator size, or -1 if unknown
	 */
	public long getSize() {
		return size;
	}

	/**
	 * Skips the given number of elements.
	 *
	 * @param n number of elements to skip
	 * @throws IllegalArgumentException if n is negative
	 * @throws NoSuchElementException if skipped past the last element
	 */
	public void skip(long n)
			throws IllegalArgumentException, NoSuchElementException {
		if (n < 0) {
			throw new IllegalArgumentException("skip(" + n + ")");
		}
		for (long i = 0; i < n; i++) {
			next();
		}
	}

	//------------------------------------------------------------< Iterator >

	/**
	 * Checks if this iterator has more elements. If there are no more
	 * elements and the size of the iterator is unknown, then the size is
	 * set to the current position. 
	 *
	 * @return <code>true</code> if this iterator has more elements,
	 *         <code>false</code> otherwise
	 */
	public boolean hasNext() {
		if (iterator.hasNext()) {
			return true;
		} else {
			if (size == -1) {
				size = position;
			}
			return false;
		}
	}

	/**
	 * Returns the next element in this iterator and advances the iterator
	 * position. If there are no more elements and the size of the iterator
	 * is unknown, then the size is set to the current position.
	 *
	 * @return next element
	 * @throws NoSuchElementException if there are no more elements
	 */
	public Object next() throws NoSuchElementException {
		try {
			Object next = iterator.next();
			position++;
			return next;
		} catch (NoSuchElementException e) {
			if (size == -1) {
				size = position;
			}
			throw e;
		}
	}

	/**
	 * Removes the previously retrieved element. Decreases the current
	 * position and size of this iterator.
	 *
	 * @throws UnsupportedOperationException if removes are not permitted
	 * @throws IllegalStateException if there is no previous element to remove
	 */
	public void remove()
			throws UnsupportedOperationException, IllegalStateException {
		iterator.remove();
		position--;
		if (size != -1) {
			size--;
		}
	}

}