| /* |
| * 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.accumulo.core.util; |
| |
| import java.util.Iterator; |
| |
| public class PeekingIterator<E> implements Iterator<E> { |
| |
| boolean isInitialized; |
| Iterator<E> source; |
| E top; |
| |
| public PeekingIterator(Iterator<E> source) { |
| this.source = source; |
| if (source.hasNext()) |
| top = source.next(); |
| else |
| top = null; |
| isInitialized = true; |
| } |
| |
| /** |
| * Creates an uninitialized instance. This should be used in conjunction with |
| * {@link #initialize(Iterator)}. |
| */ |
| public PeekingIterator() { |
| isInitialized = false; |
| } |
| |
| /** |
| * Initializes this iterator, to be used with {@link #PeekingIterator()}. |
| */ |
| public PeekingIterator<E> initialize(Iterator<E> source) { |
| this.source = source; |
| if (source.hasNext()) |
| top = source.next(); |
| else |
| top = null; |
| isInitialized = true; |
| return this; |
| } |
| |
| public E peek() { |
| if (!isInitialized) |
| throw new IllegalStateException("Iterator has not yet been initialized"); |
| return top; |
| } |
| |
| @Override |
| public E next() { |
| if (!isInitialized) |
| throw new IllegalStateException("Iterator has not yet been initialized"); |
| E lastPeeked = top; |
| if (source.hasNext()) |
| top = source.next(); |
| else |
| top = null; |
| return lastPeeked; |
| } |
| |
| @Override |
| public void remove() { |
| throw new UnsupportedOperationException(); |
| } |
| |
| @Override |
| public boolean hasNext() { |
| if (!isInitialized) |
| throw new IllegalStateException("Iterator has not yet been initialized"); |
| return top != null; |
| } |
| } |