org.apache.pig.impl.plan

Class DepthFirstWalker<O extends Operator,P extends OperatorPlan<O>>

java.lang.Object

org.apache.pig.impl.plan.PlanWalker<O,P>

org.apache.pig.impl.plan.DepthFirstWalker<O,P>

public class DepthFirstWalker<O extends Operator,P extends OperatorPlan<O>>
extends PlanWalker<O,P>

DepthFirstWalker traverses a plan in a depth first manner. One important note is that, in compliance with the PlanWalker contract, it only visits each node in the graph once.

Field Summary

Fields inherited from class org.apache.pig.impl.plan.PlanWalker

mPlan

Constructor Summary

Constructors

Constructor and Description
DepthFirstWalker(P plan)

Method Summary

Modifier and Type	Method and Description
PlanWalker<O,P>	spawnChildWalker(P plan) Return a new instance of this same type of walker for a subplan.
void	walk(PlanVisitor<O,P> visitor) Begin traversing the graph.

Methods inherited from class org.apache.pig.impl.plan.PlanWalker

getPlan, setPlan

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DepthFirstWalker

public DepthFirstWalker(P plan)

Parameters:

plan - Plan for this walker to traverse.

Method Detail

walk

public void walk(PlanVisitor<O,P> visitor)
          throws VisitorException

Begin traversing the graph.

Specified by:

walk in class PlanWalker<O extends Operator,P extends OperatorPlan<O>>

Parameters:

visitor - Visitor this walker is being used by.

Throws:

VisitorException - if an error is encountered while walking.

spawnChildWalker

public PlanWalker<O,P> spawnChildWalker(P plan)

Description copied from class: PlanWalker

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.

Specified by:

spawnChildWalker in class PlanWalker<O extends Operator,P extends OperatorPlan<O>>

Parameters:

plan - Plan for the new walker.

Returns:

Instance of the same type of walker with mPlan set to plan.