001/* 002 * Copyright (c) 2016-2017 Chris K Wensel <chris@wensel.net>. All Rights Reserved. 003 * Copyright (c) 2007-2017 Xplenty, Inc. All Rights Reserved. 004 * 005 * Project and contact information: http://www.cascading.org/ 006 * 007 * This file is part of the Cascading project. 008 * 009 * Licensed under the Apache License, Version 2.0 (the "License"); 010 * you may not use this file except in compliance with the License. 011 * You may obtain a copy of the License at 012 * 013 * http://www.apache.org/licenses/LICENSE-2.0 014 * 015 * Unless required by applicable law or agreed to in writing, software 016 * distributed under the License is distributed on an "AS IS" BASIS, 017 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 018 * See the License for the specific language governing permissions and 019 * limitations under the License. 020 */ 021 022package cascading.util; 023 024import java.util.Iterator; 025 026/** 027 * Class SingleValueIterator is a convenience to creating an {@link Iterator} that returns one value for use 028 * with interfaces that only accept Iterator instances. 029 * <p> 030 * If given a {@code null} value, it will be assumed this Iterator instance has no value, and {@link #hasNext()} 031 * will return false. 032 */ 033public class SingleValueIterator<Value> implements Iterator<Value> 034 { 035 public static final SingleValueIterator EMPTY = new SingleValueIterator(); 036 037 private boolean hasValue = true; 038 protected Value value; 039 040 public SingleValueIterator() 041 { 042 this.hasValue = false; 043 } 044 045 public SingleValueIterator( Value value ) 046 { 047 this.hasValue = value != null; 048 this.value = value; 049 } 050 051 @Override 052 public boolean hasNext() 053 { 054 return hasValue; 055 } 056 057 @Override 058 public Value next() 059 { 060 if( !hasValue ) 061 throw new IllegalStateException( "no value available" ); 062 063 try 064 { 065 return value; 066 } 067 finally 068 { 069 hasValue = false; 070 } 071 } 072 073 @Override 074 public void remove() 075 { 076 throw new UnsupportedOperationException( "unimplimented" ); 077 } 078 079 public void reset( Value value ) 080 { 081 this.hasValue = value != null; 082 this.value = value; 083 } 084 }