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    }