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