org.apache.pig.impl.plan.PlanWalker Maven / Gradle / Ivy
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* 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.impl.plan;
/**
* PlanWalker encapsulates the logic to traverse a plan. It is used only by
* visitors.
*
* All walkers must be constructed in a way that they only visit a given node
* once in a traversal.
*/
public abstract class PlanWalker > {
protected P mPlan;
/**
* @param plan Plan for this walker to traverse.
*/
public PlanWalker(P plan) {
mPlan = 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 VisitorException;
/**
* 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 mPlan set to plan.
*/
public abstract PlanWalker spawnChildWalker(P plan);
public P getPlan() {
return mPlan ;
}
public void setPlan(P plan) {
mPlan = plan;
}
}