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.GwtCompatible; 201d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 211d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringertimport java.util.NoSuchElementException; 221d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 231d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringertimport javax.annotation.Nullable; 241d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 251d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert/** 261d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * This class provides a skeletal implementation of the {@code Iterator} 271d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * interface for sequences whose next element can always be derived from the 281d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * previous element. Null elements are not supported, nor is the 291d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * {@link #remove()} method. 301d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * 311d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * <p>Example: <pre> {@code 321d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * 337dd252788645e940eada959bdde927426e2531c9Paul Duffin * Iterator<Integer> powersOfTwo = 347dd252788645e940eada959bdde927426e2531c9Paul Duffin * new AbstractSequentialIterator<Integer>(1) { 357dd252788645e940eada959bdde927426e2531c9Paul Duffin * protected Integer computeNext(Integer previous) { 367dd252788645e940eada959bdde927426e2531c9Paul Duffin * return (previous == 1 << 30) ? null : previous * 2; 377dd252788645e940eada959bdde927426e2531c9Paul Duffin * } 387dd252788645e940eada959bdde927426e2531c9Paul Duffin * };}</pre> 391d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * 401d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * @author Chris Povirk 417dd252788645e940eada959bdde927426e2531c9Paul Duffin * @since 12.0 (in Guava as {@code AbstractLinkedIterator} since 8.0) 421d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert */ 431d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert@GwtCompatible 440888a09821a98ac0680fad765217302858e70fa4Paul Duffinpublic abstract class AbstractSequentialIterator<T> 450888a09821a98ac0680fad765217302858e70fa4Paul Duffin extends UnmodifiableIterator<T> { 461d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert private T nextOrNull; 471d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 481d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert /** 491d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * Creates a new iterator with the given first element, or, if {@code 501d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * firstOrNull} is null, creates a new empty iterator. 511d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert */ 527dd252788645e940eada959bdde927426e2531c9Paul Duffin protected AbstractSequentialIterator(@Nullable T firstOrNull) { 531d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert this.nextOrNull = firstOrNull; 541d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 551d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 561d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert /** 571d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * Returns the element that follows {@code previous}, or returns {@code null} 581d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * if no elements remain. This method is invoked during each call to 591d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * {@link #next()} in order to compute the result of a <i>future</i> call to 601d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert * {@code next()}. 611d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert */ 621d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert protected abstract T computeNext(T previous); 631d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 640888a09821a98ac0680fad765217302858e70fa4Paul Duffin @Override 651d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert public final boolean hasNext() { 661d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert return nextOrNull != null; 671d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 681d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert 690888a09821a98ac0680fad765217302858e70fa4Paul Duffin @Override 701d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert public final T next() { 711d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert if (!hasNext()) { 721d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert throw new NoSuchElementException(); 731d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 741d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert try { 751d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert return nextOrNull; 761d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } finally { 771d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert nextOrNull = computeNext(nextOrNull); 781d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 791d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert } 801d580d0f6ee4f21eb309ba7b509d2c6d671c4044Bjorn Bringert} 81