001/*
002 * Copyright (c) 2007-2017 Xplenty, Inc. All Rights Reserved.
003 *
004 * Project and contact information: http://www.cascading.org/
005 *
006 * This file is part of the Cascading project.
007 *
008 * Licensed under the Apache License, Version 2.0 (the "License");
009 * you may not use this file except in compliance with the License.
010 * You may obtain a copy of the License at
011 *
012 *     http://www.apache.org/licenses/LICENSE-2.0
013 *
014 * Unless required by applicable law or agreed to in writing, software
015 * distributed under the License is distributed on an "AS IS" BASIS,
016 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
017 * See the License for the specific language governing permissions and
018 * limitations under the License.
019 */
020
021package cascading.util;
022
023import java.util.Iterator;
024
025/**
026 * Class SingleValueIterator is a convenience to creating an {@link Iterator} that returns one value for use
027 * with interfaces that only accept Iterator instances.
028 * <p/>
029 * If given a {@code null} value, it will be assumed this Iterator instance has no value, and {@link #hasNext()}
030 * will return false.
031 */
032public class SingleValueIterator<Value> implements Iterator<Value>
033  {
034  public static final SingleValueIterator EMPTY = new SingleValueIterator();
035
036  private boolean hasValue = true;
037  protected Value value;
038
039  public SingleValueIterator()
040    {
041    this.hasValue = false;
042    }
043
044  public SingleValueIterator( Value value )
045    {
046    this.hasValue = value != null;
047    this.value = value;
048    }
049
050  @Override
051  public boolean hasNext()
052    {
053    return hasValue;
054    }
055
056  @Override
057  public Value next()
058    {
059    if( !hasValue )
060      throw new IllegalStateException( "no value available" );
061
062    try
063      {
064      return value;
065      }
066    finally
067      {
068      hasValue = false;
069      }
070    }
071
072  @Override
073  public void remove()
074    {
075    throw new UnsupportedOperationException( "unimplimented" );
076    }
077
078  public void reset( Value value )
079    {
080    this.hasValue = value != null;
081    this.value = value;
082    }
083  }