/*
* Copyright 2015-2017 the original author or 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 org.springframework.statemachine.support.tree;
import java.util.Iterator;
import java.util.NoSuchElementException;
import org.springframework.util.Assert;
public abstract class AbstractIterator<T> implements Iterator<T> {
private State state = State.NOT_READY;
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() {
Assert.state(state != State.FAILED, "State should not be FAILED");
switch (state) {
case DONE:
return false;
case READY:
return true;
default:
}
return tryToComputeNext();
}
private boolean tryToComputeNext() {
state = State.FAILED;
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;
T result = next;
next = null;
return result;
}
public final T peek() {
if (!hasNext()) {
throw new NoSuchElementException();
}
return next;
}
public final void remove() {
throw new UnsupportedOperationException("remove");
}
}