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/*
 * Copyright (C) 2010 The Guava 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.google.common.collect;

import com.google.common.annotations.GwtCompatible;
import java.util.NoSuchElementException;
import javax.annotation.CheckForNull;

/**
 * This class provides a skeletal implementation of the {@code Iterator} interface for sequences
 * whose next element can always be derived from the previous element. Null elements are not
 * supported, nor is the {@link #remove()} method.
 *
 * 

Example: * *

{@code
 * Iterator powersOfTwo =
 *     new AbstractSequentialIterator(1) {
 *       protected Integer computeNext(Integer previous) {
 *         return (previous == 1 << 30) ? null : previous * 2;
 *       }
 *     };
 * }
* * @author Chris Povirk * @since 12.0 (in Guava as {@code AbstractLinkedIterator} since 8.0) */ @GwtCompatible @ElementTypesAreNonnullByDefault public abstract class AbstractSequentialIterator extends UnmodifiableIterator { @CheckForNull private T nextOrNull; /** * Creates a new iterator with the given first element, or, if {@code firstOrNull} is null, * creates a new empty iterator. */ protected AbstractSequentialIterator(@CheckForNull T firstOrNull) { this.nextOrNull = firstOrNull; } /** * Returns the element that follows {@code previous}, or returns {@code null} if no elements * remain. This method is invoked during each call to {@link #next()} in order to compute the * result of a future call to {@code next()}. */ @CheckForNull protected abstract T computeNext(T previous); @Override public final boolean hasNext() { return nextOrNull != null; } @Override public final T next() { if (nextOrNull == null) { throw new NoSuchElementException(); } T oldNext = nextOrNull; nextOrNull = computeNext(oldNext); return oldNext; } }




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