| /* |
| * 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 org.apache.calcite.rel; |
| |
| /** |
| * A <code>RelVisitor</code> is a Visitor role in the |
| * {@link 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 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, |
| RelNode parent) { |
| node.childrenAccept(this); |
| } |
| |
| /** |
| * Replaces the root node of this traversal. |
| * |
| * @param node The new root node |
| */ |
| public void replaceRoot(RelNode node) { |
| this.root = node; |
| } |
| |
| /** |
| * Starts an iteration. |
| */ |
| public RelNode go(RelNode p) { |
| this.root = p; |
| visit(p, 0, null); |
| return root; |
| } |
| } |
| |
| // End RelVisitor.java |