/*
* Copyright 2015 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.ArrayDeque;
import java.util.Iterator;
import org.springframework.util.Assert;
public abstract class TreeTraverser<T> {
/**
* Returns the children of the specified node. Must not contain null.
*
* @param root the node
* @return child iterables
*/
public abstract Iterable<T> children(T root);
public final Iterable<T> postOrderTraversal(final T root) {
Assert.notNull(root, "root should not be null");
return new Iterable<T>() {
@Override
public Iterator<T> iterator() {
return postOrderIterator(root);
}
};
}
Iterator<T> postOrderIterator(T root) {
return new PostOrderIterator(root);
}
private static final class PostOrderNode<T> {
final T root;
final Iterator<T> childIterator;
PostOrderNode(T root, Iterator<T> childIterator) {
Assert.notNull(root, "root should not be null");
Assert.notNull(childIterator, "childIterator should not be null");
this.root = root;
this.childIterator = childIterator;
}
}
private final class PostOrderIterator extends AbstractIterator<T> {
private final ArrayDeque<PostOrderNode<T>> stack;
PostOrderIterator(T root) {
this.stack = new ArrayDeque<PostOrderNode<T>>();
stack.addLast(expand(root));
}
@Override
protected T computeNext() {
while (!stack.isEmpty()) {
PostOrderNode<T> top = stack.getLast();
if (top.childIterator.hasNext()) {
T child = top.childIterator.next();
stack.addLast(expand(child));
} else {
stack.removeLast();
return top.root;
}
}
return endOfData();
}
private PostOrderNode<T> expand(T t) {
return new PostOrderNode<T>(t, children(t).iterator());
}
}
}