| /* |
| * 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.pig.newplan; |
| |
| import org.apache.pig.impl.logicalLayer.FrontendException; |
| |
| public abstract class PlanWalker { |
| |
| protected OperatorPlan plan; |
| |
| /** |
| * @param plan Plan for this walker to traverse. |
| */ |
| public PlanWalker(OperatorPlan plan) { |
| this.plan = plan; |
| } |
| |
| /** |
| * Begin traversing the graph. |
| * @param visitor Visitor this walker is being used by. This can't be set in |
| * the constructor because the visitor is constructing this class, and does |
| * not yet have a 'this' pointer to send as an argument. |
| * @throws VisitorException if an error is encountered while walking. |
| */ |
| public abstract void walk(PlanVisitor visitor) throws FrontendException; |
| |
| /** |
| * Return a new instance of this same type of walker for a subplan. |
| * When this method is called the same type of walker with the |
| * provided plan set as the plan, must be returned. This can then be |
| * used to walk subplans. This allows abstract visitors to clone |
| * walkers without knowning the type of walker their subclasses used. |
| * @param plan Plan for the new walker. |
| * @return Instance of the same type of walker with plan set to plan. |
| */ |
| public abstract PlanWalker spawnChildWalker(OperatorPlan plan); |
| |
| public OperatorPlan getPlan() { |
| return plan ; |
| } |
| |
| /** |
| * Set the plan for this walker to operate on. |
| * @param plan to walk |
| */ |
| public void setPlan(OperatorPlan plan) { |
| this.plan = plan; |
| } |
| |
| } |