1/*
2 * Copyright (C) 2007 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.google.common.base;
18
19import static com.google.common.base.Preconditions.checkState;
20
21import com.google.common.annotations.GwtCompatible;
22
23import java.util.Iterator;
24import java.util.NoSuchElementException;
25
26/**
27 * Note this class is a copy of
28 * {@link com.google.common.collect.AbstractIterator} (for dependency reasons).
29 */
30@GwtCompatible
31abstract class AbstractIterator<T> implements Iterator<T> {
32  private State state = State.NOT_READY;
33
34  protected AbstractIterator() {}
35
36  private enum State {
37    READY, NOT_READY, DONE, FAILED,
38  }
39
40  private T next;
41
42  protected abstract T computeNext();
43
44  protected final T endOfData() {
45    state = State.DONE;
46    return null;
47  }
48
49  @Override
50  public final boolean hasNext() {
51    checkState(state != State.FAILED);
52    switch (state) {
53      case DONE:
54        return false;
55      case READY:
56        return true;
57      default:
58    }
59    return tryToComputeNext();
60  }
61
62  private boolean tryToComputeNext() {
63    state = State.FAILED; // temporary pessimism
64    next = computeNext();
65    if (state != State.DONE) {
66      state = State.READY;
67      return true;
68    }
69    return false;
70  }
71
72  @Override
73  public final T next() {
74    if (!hasNext()) {
75      throw new NoSuchElementException();
76    }
77    state = State.NOT_READY;
78    return next;
79  }
80
81  @Override public final void remove() {
82    throw new UnsupportedOperationException();
83  }
84}
85