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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.Beta;
import com.google.common.annotations.GwtCompatible;
import java.util.NoSuchElementException;
import javax.annotation.Nullable;
/**
* 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.
*
* <p>Example: <pre> {@code
*
* Iterator<Integer> powersOfTwo = new AbstractLinkedIterator<Integer>(1) {
* protected Integer computeNext(Integer previous) {
* return (previous == 1 << 30) ? null : previous * 2;
* }
* };}</pre>
*
* @author Chris Povirk
* @since 8.0
*/
@Beta
@GwtCompatible
public abstract class AbstractLinkedIterator<T>
extends UnmodifiableIterator<T> {
private T nextOrNull;
/**
* Creates a new iterator with the given first element, or, if {@code
* firstOrNull} is null, creates a new empty iterator.
*/
protected AbstractLinkedIterator(@Nullable 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 <i>future</i> call to
* {@code next()}.
*/
protected abstract T computeNext(T previous);
@Override
public final boolean hasNext() {
return nextOrNull != null;
}
@Override
public final T next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
try {
return nextOrNull;
} finally {
nextOrNull = computeNext(nextOrNull);
}
}
}
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