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The Apache Commons Collections package contains types that extend and augment the Java Collections Framework.

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/*
 * 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
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 * governing permissions and limitations under the License.
 */
package org.apache.commons.collections4.iterators;

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

/**
 * Decorates another iterator to return elements in a specific range.
 * 

* The decorated iterator is bounded in the range [offset, offset+max). * The {@code offset} corresponds to the position of the first element to * be returned from the decorated iterator, and {@code max} is the maximum * number of elements to be returned at most. *

* In case an offset parameter other than 0 is provided, the decorated * iterator is immediately advanced to this position, skipping all elements * before that position. * * @since 4.1 */ public class BoundedIterator implements Iterator { /** The iterator being decorated. */ private final Iterator iterator; /** The offset to bound the first element return */ private final long offset; /** The max number of elements to return */ private final long max; /** The position of the current element */ private long pos; //----------------------------------------------------------------------- /** * Decorates the specified iterator to return at most the given number of elements, * skipping all elements until the iterator reaches the position at {@code offset}. *

* The iterator is immediately advanced until it reaches the position at {@code offset}, * incurring O(n) time. * * @param iterator the iterator to be decorated * @param offset the index of the first element of the decorated iterator to return * @param max the maximum number of elements of the decorated iterator to return * @throws NullPointerException if iterator is null * @throws IllegalArgumentException if either offset or max is negative */ public BoundedIterator(final Iterator iterator, final long offset, final long max) { if (iterator == null) { throw new NullPointerException("Iterator must not be null"); } if (offset < 0) { throw new IllegalArgumentException("Offset parameter must not be negative."); } if (max < 0) { throw new IllegalArgumentException("Max parameter must not be negative."); } this.iterator = iterator; this.offset = offset; this.max = max; pos = 0; init(); } /** * Advances the underlying iterator to the beginning of the bounded range. */ private void init() { while (pos < offset && iterator.hasNext()) { iterator.next(); pos++; } } //----------------------------------------------------------------------- @Override public boolean hasNext() { if (!checkBounds()) { return false; } return iterator.hasNext(); } /** * Checks whether the iterator is still within its bounded range. * @return {@code true} if the iterator is within its bounds, {@code false} otherwise */ private boolean checkBounds() { if (pos - offset + 1 > max) { return false; } return true; } @Override public E next() { if (!checkBounds()) { throw new NoSuchElementException(); } final E next = iterator.next(); pos++; return next; } /** * {@inheritDoc} *

* In case an offset other than 0 was specified, the underlying iterator will be advanced * to this position upon creation. A call to {@link #remove()} will still result in an * {@link IllegalStateException} if no explicit call to {@link #next()} has been made prior * to calling {@link #remove()}. */ @Override public void remove() { if (pos <= offset) { throw new IllegalStateException("remove() can not be called before calling next()"); } iterator.remove(); } }





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