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 com.clearspring.analytics.util;
  
  import java.util.Iterator;
  import java.util.NoSuchElementException;
  
  /**
   * Rough and ready clone of the Guava AbstractIterator.  I just did this
   * to avoid needing to add the guava dependency.  It would be better to
   * just use quava.
   */
  public abstract class AbstractIterator<T> implements Iterator<T> {
  
      private enum State {
          NOT_STARTED, DONE, HAS_DATA, EMPTY
      }
  
      private T next;
  
      private State currentState = State.NOT_STARTED;
  
      @Override
      public boolean hasNext() {
          switch (currentState) {
              case DONE:
                  return false;
              case NOT_STARTED:
                  currentState = State.HAS_DATA;
                  next = computeNext();
                  break;
              case HAS_DATA:
                  return true;
              case EMPTY:
                  currentState = State.HAS_DATA;
                  next = computeNext();
                  break;
          }
          return currentState != State.DONE;
      }
  
      @Override
      public T next() {
          if (hasNext()) {
              T r = next;
              currentState = State.EMPTY;
              return r;
          } else {
              throw new NoSuchElementException();
          }
      }
  
      @Override
      public void remove() {
          throw new UnsupportedOperationException("Can't remove from an abstract iterator");
      }
  
      protected abstract T computeNext();
  
      public T endOfData() {
          currentState = State.DONE;
          return null;
      }
  }
  