Apache Derby Database Engine and Embedded JDBC Driver 10.17.1.0 · org.apache.derby.iapi.sql.compile.Visitor

Method Summary

Modifier and Type	Method and Description
public boolean	Returns: true/false skipChildren(Visitable the node to process node) Method that is called to indicate whether we should skip all nodes below this node for traversal.
public boolean	Returns: true/false stopTraversal() Method that is called to see if query tree traversal should be stopped before visiting all nodes.
public Visitable	Returns: a query tree node. Often times this is the same node that was passed in, but Visitors that replace nodes with other nodes will use this to return the new replacement node. visit(Visitable the node to process node) This is the default visit operation on a QueryTreeNode.
public boolean	Returns: `true` if `node`'s children should be visited before `node`, `false` otherwise visitChildrenFirst(Visitable the top node of a sub-tree about to be visited node) Method that is called to see if `visit()` should be called on the children of `node` before it is called on `node` itself.

Method Detail

skipChildren	back to summary
public boolean skipChildren(Visitable node) throws StandardException Method that is called to indicate whether we should skip all nodes below this node for traversal. Useful if we want to effectively ignore/prune all branches under a particular node. Differs from stopTraversal() in that it only affects subtrees, rather than the entire traversal. Parameters node:Visitable the node to process Returns:boolean true/false

skipChildren

back to summary

public boolean skipChildren(Visitable node) throws StandardException

Method that is called to indicate whether we should skip all nodes below this node for traversal. Useful if we want to effectively ignore/prune all branches under a particular node.

Differs from stopTraversal() in that it only affects subtrees, rather than the entire traversal.

Parameters

node:Visitable: the node to process

Returns:boolean

true/false

stopTraversal	back to summary
public boolean stopTraversal() Method that is called to see if query tree traversal should be stopped before visiting all nodes. Useful for short circuiting traversal if we already know we are done. Returns:boolean true/false

stopTraversal

back to summary

public boolean stopTraversal()

Method that is called to see if query tree traversal should be stopped before visiting all nodes. Useful for short circuiting traversal if we already know we are done.

Returns:boolean: true/false

visit	back to summary
public Visitable visit(Visitable node) throws StandardException This is the default visit operation on a QueryTreeNode. It just returns the node. This will typically suffice as the default visit operation for most visitors unless the visitor needs to count the number of nodes visited or something like that. Visitors will overload this method by implementing a version with a signature that matches a specific type of node. For example, if I want to do something special with aggregate nodes, then that Visitor will implement a visit(AggregateNode node) method which does the aggregate specific processing. Parameters node:Visitable the node to process Returns:Visitable a query tree node. Often times this is the same node that was passed in, but Visitors that replace nodes with other nodes will use this to return the new replacement node. Exceptions StandardException: may be throw an error as needed by the visitor (i.e. may be a normal error if a particular node is found, e.g. if checking a group by, we don't expect to find any ColumnReferences that aren't under an AggregateNode -- the easiest thing to do is just throw an error when we find the questionable node).

visit

back to summary

public Visitable visit(Visitable node) throws StandardException

This is the default visit operation on a QueryTreeNode. It just returns the node. This will typically suffice as the default visit operation for most visitors unless the visitor needs to count the number of nodes visited or something like that.

Visitors will overload this method by implementing a version with a signature that matches a specific type of node. For example, if I want to do something special with aggregate nodes, then that Visitor will implement a visit(AggregateNode node) method which does the aggregate specific processing.

Parameters

node:Visitable: the node to process

Returns:Visitable

a query tree node. Often times this is the same node that was passed in, but Visitors that replace nodes with other nodes will use this to return the new replacement node.

Exceptions

StandardException:: may be throw an error as needed by the visitor (i.e. may be a normal error if a particular node is found, e.g. if checking a group by, we don't expect to find any ColumnReferences that aren't under an AggregateNode -- the easiest thing to do is just throw an error when we find the questionable node).

visitChildrenFirst back to summary

visitChildrenFirst	back to summary
public boolean visitChildrenFirst(Visitable node) Method that is called to see if `visit()` should be called on the children of `node` before it is called on `node` itself. If this method always returns `true`, the visitor will walk the tree bottom-up. If it always returns `false`, the tree is visited top-down. Parameters node:Visitable the top node of a sub-tree about to be visited Returns:boolean `true` if `node`'s children should be visited before `node`, `false` otherwise

public boolean visitChildrenFirst(Visitable node)

Method that is called to see if visit() should be called on the children of node before it is called on node itself. If this method always returns true, the visitor will walk the tree bottom-up. If it always returns false, the tree is visited top-down.

Parameters

node:Visitable: the top node of a sub-tree about to be visited

Returns:boolean

true if node's children should be visited before node, false otherwise

public Interface Visitor

Method Summary

Method Detail