    001    /*
    002     * Copyright (C) 2010 The Guava Authors
    003     *
    004     * Licensed under the Apache License, Version 2.0 (the "License");
    005     * you may not use this file except in compliance with the License.
    006     * You may obtain a copy of the License at
    007     *
    008     * http://www.apache.org/licenses/LICENSE-2.0
    009     *
    010     * Unless required by applicable law or agreed to in writing, software
    011     * distributed under the License is distributed on an "AS IS" BASIS,
    012     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    013     * See the License for the specific language governing permissions and
    014     * limitations under the License.
    015     */
    016
    017    package com.google.common.collect;
    018
    019    import com.google.common.annotations.Beta;
    020    import com.google.common.annotations.GwtCompatible;
    021
    022    import java.util.NoSuchElementException;
    023
    024    import javax.annotation.Nullable;
    025
    026    /**
    027     * This class provides a skeletal implementation of the {@code Iterator}
    028     * interface for sequences whose next element can always be derived from the
    029     * previous element. Null elements are not supported, nor is the
    030     * {@link #remove()} method.
    031     *
    032     * <p>Example: <pre>   {@code
    033     *
    034     *   Iterator<Integer> powersOfTwo = new AbstractLinkedIterator<Integer>(1) {
    035     *     protected Integer computeNext(Integer previous) {
    036     *       return (previous == 1 << 30) ? null : previous * 2;
    037     *     }
    038     *   };}</pre>
    039     *
    040     * @author Chris Povirk
    041     * @since 8.0
    042     * @deprecated This class has been renamed {@link AbstractSequentialIterator}.
    043     *     This class is scheduled to be removed in Guava release 13.0.
    044     */
    045    @Beta
    046    @Deprecated
    047    @GwtCompatible
    048    public abstract class AbstractLinkedIterator<T>
    049        extends UnmodifiableIterator<T> {
    050      private T nextOrNull;
    051
    052      /**
    053       * Creates a new iterator with the given first element, or, if {@code
    054       * firstOrNull} is null, creates a new empty iterator.
    055       */
    056      protected AbstractLinkedIterator(@Nullable T firstOrNull) {
    057        this.nextOrNull = firstOrNull;
    058      }
    059
    060      /**
    061       * Returns the element that follows {@code previous}, or returns {@code null}
    062       * if no elements remain. This method is invoked during each call to
    063       * {@link #next()} in order to compute the result of a <i>future</i> call to
    064       * {@code next()}.
    065       */
    066      protected abstract T computeNext(T previous);
    067
    068      @Override
    069      public final boolean hasNext() {
    070        return nextOrNull != null;
    071      }
    072
    073      @Override
    074      public final T next() {
    075        if (!hasNext()) {
    076          throw new NoSuchElementException();
    077        }
    078        try {
    079          return nextOrNull;
    080        } finally {
    081          nextOrNull = computeNext(nextOrNull);
    082        }
    083      }
    084    }