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/*
* Copyright (C) 2007 The Guava Authors
*
* Licensed 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 com.google.common.base;
import static com.google.common.base.Preconditions.checkState;
import com.google.common.annotations.GwtCompatible;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* Note this class is a copy of
* {@link com.google.common.collect.AbstractIterator} (for dependency reasons).
*/
@GwtCompatible
abstract class AbstractIterator<T> implements Iterator<T> {
private State state = State.NOT_READY;
protected AbstractIterator() {}
private enum State {
READY, NOT_READY, DONE, FAILED,
}
private T next;
protected abstract T computeNext();
protected final T endOfData() {
state = State.DONE;
return null;
}
@Override
public final boolean hasNext() {
checkState(state != State.FAILED);
switch (state) {
case DONE:
return false;
case READY:
return true;
default:
}
return tryToComputeNext();
}
private boolean tryToComputeNext() {
state = State.FAILED; // temporary pessimism
next = computeNext();
if (state != State.DONE) {
state = State.READY;
return true;
}
return false;
}
@Override
public final T next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
state = State.NOT_READY;
return next;
}
@Override public final void remove() {
throw new UnsupportedOperationException();
}
}
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