/*
 * 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 org.checkerframework.checker.nullness.qual.Nullable;

This class provides a skeletal implementation of the Iterator interface for sequences whose next element can always be derived from the previous element. Null elements are not supported, nor is the UnmodifiableIterator.remove() method.

Example:


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