| /* |
| * 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> |
| { |
| |
| 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(); |
| } |
| } |