Java tutorial
/* * Copyright (C) 2015-2015 The Helenus Driver Project Authors. * * Licensed 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 com.github.helenusdriver.commons.collections.iterators; import java.io.Serializable; import java.util.ArrayList; import java.util.Collections; import java.util.Iterator; import java.util.List; import java.util.Map; import java.util.NoSuchElementException; import org.apache.commons.collections4.ResettableIterator; /** * The <code>SnapshotIterator</code> class provides support for creating a * snapshot from another iterator; preserving the order of returned elements. * <p> * <i>Note:</i> An instance of this class can be properly serialized even if * the iterator object passed to its constructor is not serializable as long * as its elements are serializable. If the elements are of type * {@link java.util.Map.Entry}, then they will be cloned and made serializable * as long as the associated keys and values are serializable. * <p> * The implementation provided here takes a snapshot of all elements returned * by the given iterator by iterating them and then releasing the iterator. * * @copyright 2015-2015 The Helenus Driver Project Authors * * @author The Helenus Driver Project Authors * @version 1 - Jan 15, 2015 - paouelle - Creation * * @param <T> the type of elements iterated by the iterator * * @since 1.0 */ public class SnapshotIterator<T> implements ResettableIterator<T>, Serializable { /** * Holds the serialVersionUID. * * @author paouelle */ private static final long serialVersionUID = 5564723343035529469L; /** * Holds the elements to iterate. * * @author paouelle * * @serial the list of elements being iterated */ private final List<T> list; /** * Holds the current index for the iterator. * * @author paouelle * * @serial the current index for the iterator */ private int current = 0; /** * Instantiates a new <code>SnapshotIterator</code> object. * * @author paouelle * * @param i the iterator to create a snapshot for * @throws NullPointerException if <code>i</code> is <code>null</code> */ @SuppressWarnings({ "unchecked", "rawtypes" }) public SnapshotIterator(Iterator<T> i) { org.apache.commons.lang3.Validate.notNull(i, "invalid null iterator"); if (!i.hasNext()) { this.list = Collections.emptyList(); return; } this.list = new ArrayList<>(); while (i.hasNext()) { T e = i.next(); if (e instanceof Map.Entry<?, ?>) { // make sure we clone these entries to avoid someone modifying them // behind our back and also to make them serializable!!!! e = (T) new SnapshotEntry((Map.Entry<?, ?>) e); } list.add(e); } } /** * Instantiates a new <code>SnapshotIterator</code> object. * * @author paouelle * * @param i the iterable object to snapshot it's iterator * @throws NullPointerException if <code>i</code> is <code>null</code> */ public SnapshotIterator(Iterable<T> i) { this(i.iterator()); } /** * {@inheritDoc} * * @author paouelle * * @see ResettableIterator#reset() */ @Override public void reset() { this.current = 0; } /** * {@inheritDoc} * * @author paouelle * * @see java.util.Iterator#hasNext() */ @Override public boolean hasNext() { return (current < list.size()); } /** * {@inheritDoc} * * @author paouelle * * @see java.util.Iterator#next() */ @Override public T next() { if (!hasNext()) { throw new NoSuchElementException("Snapshot Iterator"); } return list.get(current++); } /** * {@inheritDoc} * * @author paouelle * * @throws UnsupportedOperationException always thrown * * @see java.util.Iterator#remove() */ @Override public void remove() { throw new UnsupportedOperationException("Snapshot Iterator"); } } /** * The <code>SnapshotEntry</code> class provides a snapshot * implementation of the {@link java.util.Map.Entry} interface. * * @copyright 2015-2015 The Helenus Driver Project Authors * * @author The Helenus Driver Project Authors * @version 1 - Jan 15, 2015 - paouelle - Creation * * @param <K> the key type * @param <V> the value type * * @since 1.0 */ final class SnapshotEntry<K, V> implements Map.Entry<K, V>, Serializable { /** * Holds the serialVersionUID. * * @author paouelle */ private static final long serialVersionUID = -5090863113841689882L; /** * Holds the entry hash code. * * @author paouelle * * @serial the hash code for the entry */ private final int hash; /** * Holds the associated key. * * @author paouelle * * @serial the key */ private final K key; /** * Holds the associated value. * * @author paouelle * * @serial the value */ private final V value; /** * Instantiates a new <code>SnapshotEntry</code> object. * * @author paouelle * * @param e the entry to be cloned * @throws NullPointerException if <code>e</code> is <code>null</code> */ SnapshotEntry(Map.Entry<K, V> e) { org.apache.commons.lang3.Validate.notNull(e, "invalid null entry"); this.hash = e.hashCode(); this.key = e.getKey(); this.value = e.getValue(); } /** * {@inheritDoc} * * @author paouelle * * @see java.util.Map.Entry#getKey() */ @Override public K getKey() { return key; } /** * {@inheritDoc} * * @author paouelle * * @see java.util.Map.Entry#getValue() */ @Override public V getValue() { return value; } /** * {@inheritDoc} * * @author paouelle * * @throws UnsupportedOperationException always thrown * * @see java.util.Map.Entry#setValue(java.lang.Object) */ @Override public V setValue(V value) { throw new UnsupportedOperationException("Snapshot Entry"); } /** * {@inheritDoc} * * @author paouelle * * @see java.lang.Object#equals(java.lang.Object) */ @Override public boolean equals(Object o) { if (!(o instanceof Map.Entry<?, ?>)) { return false; } final Map.Entry<?, ?> e = (Map.Entry<?, ?>) o; return (((key == null) ? (e.getKey() == null) : key.equals(e.getKey())) && ((value == null) ? (e.getValue() == null) : value.equals(e.getValue()))); } /** * {@inheritDoc} * * @author paouelle * * @see java.lang.Object#hashCode() */ @Override public int hashCode() { return hash; } /** * {@inheritDoc} * * @author paouelle * * @see java.lang.Object#toString() */ @Override public String toString() { return key + "=" + value; } }