86 lines
2.3 KiB
Java
86 lines
2.3 KiB
Java
/*
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* Copyright (C) 2010 The Guava Authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.google.common.collect;
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import java.util.NoSuchElementException;
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import javax.annotation.Nullable;
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import com.google.common.annotations.GwtCompatible;
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/**
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* This class provides a skeletal implementation of the {@code Iterator}
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* interface for sequences whose next element can always be derived from the
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* previous element. Null elements are not supported, nor is the
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* {@link #remove()} method.
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*
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* <p>
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* Example:
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*
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* <pre>
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* {
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* @code
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*
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* Iterator<Integer> powersOfTwo = new AbstractSequentialIterator<Integer>(1) {
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* protected Integer computeNext(Integer previous) {
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* return (previous == 1 << 30) ? null : previous * 2;
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* }
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* };
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* }
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* </pre>
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*
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* @author Chris Povirk
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* @since 12.0 (in Guava as {@code AbstractLinkedIterator} since 8.0)
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*/
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@GwtCompatible
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public abstract class AbstractSequentialIterator<T> extends UnmodifiableIterator<T> {
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private T nextOrNull;
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/**
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* Creates a new iterator with the given first element, or, if {@code
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* firstOrNull} is null, creates a new empty iterator.
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*/
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protected AbstractSequentialIterator(@Nullable T firstOrNull) {
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this.nextOrNull = firstOrNull;
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}
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/**
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* Returns the element that follows {@code previous}, or returns {@code null} if
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* no elements remain. This method is invoked during each call to
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* {@link #next()} in order to compute the result of a <i>future</i> call to
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* {@code next()}.
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*/
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protected abstract T computeNext(T previous);
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@Override
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public final boolean hasNext() {
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return nextOrNull != null;
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}
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@Override
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public final T next() {
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if (!hasNext()) {
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throw new NoSuchElementException();
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}
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try {
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return nextOrNull;
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} finally {
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nextOrNull = computeNext(nextOrNull);
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}
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}
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}
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