2021SC@SDUSC

目录

2021SC@SDUSC

PlanWalker

子类

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PlanWalker

    

package org.apache.pig.newplan;

import org.apache.pig.impl.logicalLayer.FrontendException;

public abstract class PlanWalker {

    protected OperatorPlan plan;

    
    public PlanWalker(OperatorPlan plan) {
        this.plan = plan;
    }

    
    public abstract void walk(PlanVisitor visitor) throws FrontendException;

    
    public abstract PlanWalker spawnChildWalker(OperatorPlan plan);

    public OperatorPlan getPlan() {
        return plan ;
    }
    
    
    public void setPlan(OperatorPlan plan) {
        this.plan = plan;
    }

}

PlanWalker提供的是遍历访问一个plan的能力。

子类

PlanWalker的子类主要实现两个方法：

public abstract void walk(PlanVisitor visitor) throws FrontendException;
 
public abstract PlanWalker spawnChildWalker(OperatorPlan plan);

walk()方法在子类的实现中，会以不同的顺序遍历plan，最后的结果是遍历到的节点Operator会调op.accept(visitor)接受本Visitor。