XPLAINDefaultVisitor (Apache Derby V10.14 Internals)

java.lang.Object
- org.apache.derby.impl.sql.execute.xplain.XPLAINDefaultVisitor

All Implemented Interfaces:

XPLAINVisitor
```
public class XPLAINDefaultVisitor
extends java.lang.Object
implements XPLAINVisitor
```
This is the Default Visitor which produces explain information like the old getRuntimeStatistics() approach.
It exists to support backward-compatibility. The only thing this visitor does, is to log the output of the statistics to the default log stream. (the file derby.log)

Constructor Summary

Constructors
Constructor Description

XPLAINDefaultVisitor()

Constructors
Constructor	Description
`XPLAINDefaultVisitor()`

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`void`	`doXPLAIN(RunTimeStatistics rss, Activation activation)`	This method is the hook method which is called from the TopResultSet.
`void`	`reset()`	Call this method to reset the visitor for a new run over the statistics.
`void`	`setNumberOfChildren(int noChildren)`	This method informs the visitor about the number of children.
`void`	`visit(ResultSetStatistics statistics)`	This is the Visitor hook method, which gets called from each ResultSetStatistics.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - XPLAINDefaultVisitor
```
public XPLAINDefaultVisitor()
```
- Method Detail
  - visit
```
public void visit(ResultSetStatistics statistics)
```
    Description copied from interface: XPLAINVisitor
    
    This is the Visitor hook method, which gets called from each ResultSetStatistics. It depends on the sub-class implementation of this interface, to describe the behaviour of the explanation facility.
    To be easily extendable with new explain representation methods, just implement this interface and provide the new behaviour.
    
    Specified by:
    
    visit in interface XPLAINVisitor
    
    Parameters:
    
    statistics - the statistics, which want to get explained.
  - reset
```
public void reset()
```
    Description copied from interface: XPLAINVisitor
    
    Call this method to reset the visitor for a new run over the statistics. A default implementation should call this method automatically at first of a call of doXPLAIN().
    
    Specified by:
    
    reset in interface XPLAINVisitor
  - doXPLAIN
```
public void doXPLAIN(RunTimeStatistics rss,
                     Activation activation)
```
    Description copied from interface: XPLAINVisitor
    
    This method is the hook method which is called from the TopResultSet. It starts the explanation of the current ResultSetStatistics tree and keeps the information during one explain run.
    
    Specified by:
    
    doXPLAIN in interface XPLAINVisitor
  - setNumberOfChildren
```
public void setNumberOfChildren(int noChildren)
```
    Description copied from interface: XPLAINVisitor
    
    This method informs the visitor about the number of children. It has to be called first! by the different explainable nodes before the visit method of the visitor gets called. Each node knows how many children he has. The visitor can use this information to resolve the relationship of the current explained node to above nodes. Due to the top-down, pre-order, depth-first traversal of the tree, this information can directly be exploited.
    
    Specified by:
    
    setNumberOfChildren in interface XPLAINVisitor
    
    Parameters:
    
    noChildren - the number of children of the current explained node.

Class XPLAINDefaultVisitor

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

XPLAINDefaultVisitor

Method Detail

visit

reset

doXPLAIN

setNumberOfChildren