content: /*
  * Licensed to the Apache Software Foundation (ASF) under one
  * or more contributor license agreements.  See the NOTICE file
  * distributed with this work for additional information
  * regarding copyright ownership.  The ASF licenses this file
  * to you 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 org.apache.cassandra.utils;
  
  import java.util.Iterator;
  import java.util.NoSuchElementException;
  
  import com.google.common.collect.PeekingIterator;
  
  public abstract class AbstractIterator<V> implements Iterator<V>, PeekingIterator<V>, CloseableIterator<V>
  {
  
      private static enum State { MUST_FETCH, HAS_NEXT, DONE, FAILED }
      private State state = State.MUST_FETCH;
      private V next;
  
      protected V endOfData()
      {
          state = State.DONE;
          return null;
      }
  
      protected abstract V computeNext();
  
      public boolean hasNext()
      {
          switch (state)
          {
              case MUST_FETCH:
                  state = State.FAILED;
                  next = computeNext();
  
              default:
                  if (state == State.DONE)
                      return false;
  
                  state = State.HAS_NEXT;
                  return true;
  
              case FAILED:
                  throw new IllegalStateException();
          }
      }
  
      public V next()
      {
          if (state != State.HAS_NEXT && !hasNext())
              throw new NoSuchElementException();
  
          state = State.MUST_FETCH;
          V result = next;
          next = null;
          return result;
      }
  
      public V peek()
      {
          if (!hasNext())
              throw new NoSuchElementException();
          return next;
      }
  
      public void remove()
      {
          throw new UnsupportedOperationException();
      }
  
      public void close()
      {
          //no-op
      }
  }
  