11d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert/* 21d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * Copyright (C) 2010 The Guava Authors 31d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * 41d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * Licensed under the Apache License, Version 2.0 (the "License"); 51d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * you may not use this file except in compliance with the License. 61d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * You may obtain a copy of the License at 71d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * 81d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * http://www.apache.org/licenses/LICENSE-2.0 91d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * 101d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * Unless required by applicable law or agreed to in writing, software 111d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * distributed under the License is distributed on an "AS IS" BASIS, 121d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 131d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * See the License for the specific language governing permissions and 141d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * limitations under the License. 151d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert */ 161d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 171d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringertpackage com.google.common.collect; 181d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 191d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringertimport com.google.common.annotations.Beta; 201d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringertimport com.google.common.annotations.GwtCompatible; 211d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 221d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringertimport java.util.NoSuchElementException; 231d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 241d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringertimport javax.annotation.Nullable; 251d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 261d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert/** 271d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * This class provides a skeletal implementation of the {@code Iterator} 281d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * interface for sequences whose next element can always be derived from the 291d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * previous element. Null elements are not supported, nor is the 301d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * {@link #remove()} method. 311d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * 321d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * <p>Example: <pre> {@code 331d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * 341d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * Iterator<Integer> powersOfTwo = new AbstractLinkedIterator<Integer>(1) { 351d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * protected Integer computeNext(Integer previous) { 361d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * return (previous == 1 << 30) ? null : previous * 2; 371d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * } 381d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * };}</pre> 391d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * 401d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * @author Chris Povirk 411d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * @since 8.0 421d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert */ 431d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert@Beta 441d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert@GwtCompatible 451d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringertpublic abstract class AbstractLinkedIterator<T> 461d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert extends UnmodifiableIterator<T> { 471d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert private T nextOrNull; 481d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 491d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert /** 501d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * Creates a new iterator with the given first element, or, if {@code 511d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * firstOrNull} is null, creates a new empty iterator. 521d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert */ 531d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert protected AbstractLinkedIterator(@Nullable T firstOrNull) { 541d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert this.nextOrNull = firstOrNull; 551d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 561d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 571d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert /** 581d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * Returns the element that follows {@code previous}, or returns {@code null} 591d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * if no elements remain. This method is invoked during each call to 601d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * {@link #next()} in order to compute the result of a <i>future</i> call to 611d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * {@code next()}. 621d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert */ 631d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert protected abstract T computeNext(T previous); 641d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 651d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert @Override 661d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert public final boolean hasNext() { 671d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert return nextOrNull != null; 681d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 691d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 701d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert @Override 711d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert public final T next() { 721d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert if (!hasNext()) { 731d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert throw new NoSuchElementException(); 741d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 751d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert try { 761d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert return nextOrNull; 771d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } finally { 781d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert nextOrNull = computeNext(nextOrNull); 791d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 801d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 811d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert} 82