com.hazelcast.org.apache.calcite.rel.RelVisitor Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to you 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.hazelcast.org.apache.calcite.rel;
import com.hazelcast.org.checkerframework.checker.nullness.qual.Nullable;
/**
* A RelVisitor is a Visitor role in the
* {@link com.hazelcast.org.apache.calcite.util.Glossary#VISITOR_PATTERN visitor pattern} and
* visits {@link RelNode} objects as the role of Element. Other components in
* the pattern: {@link RelNode#childrenAccept(RelVisitor)}.
*/
public abstract class RelVisitor {
//~ Instance fields --------------------------------------------------------
private @Nullable RelNode root;
//~ Methods ----------------------------------------------------------------
/**
* Visits a node during a traversal.
*
* @param node Node to visit
* @param ordinal Ordinal of node within its parent
* @param parent Parent of the node, or null if it is the root of the
* traversal
*/
public void visit(
RelNode node,
int ordinal,
@Nullable RelNode parent) {
node.childrenAccept(this);
}
/**
* Replaces the root node of this traversal.
*
* @param node The new root node
*/
public void replaceRoot(@Nullable RelNode node) {
this.root = node;
}
/**
* Starts an iteration.
*/
public @Nullable RelNode go(RelNode p) {
this.root = p;
visit(p, 0, null);
return root;
}
}