org.antlr.v4.runtime.tree

Class AbstractParseTreeVisitor<T>

java.lang.Object

org.antlr.v4.runtime.tree.AbstractParseTreeVisitor<T>

All Implemented Interfaces:

ParseTreeVisitor<T>

public abstract class AbstractParseTreeVisitor<T>
extends java.lang.Object
implements ParseTreeVisitor<T>

Constructor Summary

Constructors

Constructor and Description
AbstractParseTreeVisitor()

Method Summary

Modifier and Type	Method and Description
protected T	aggregateResult(T aggregate, T nextResult) Aggregates the results of visiting multiple children of a node.
protected T	defaultResult() Gets the default value returned by visitor methods.
protected boolean	shouldVisitNextChild(RuleNode node, T currentResult) This method is called after visiting each child in visitChildren(org.antlr.v4.runtime.tree.RuleNode).
T	visit(ParseTree tree) Visit a parse tree, and return a user-defined result of the operation.
T	visitChildren(RuleNode node) Visit the children of a node, and return a user-defined result of the operation.
T	visitErrorNode(ErrorNode node) Visit an error node, and return a user-defined result of the operation.
T	visitTerminal(TerminalNode node) Visit a terminal node, and return a user-defined result of the operation.

Methods inherited from class java.lang.Object

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

Constructor Detail

AbstractParseTreeVisitor

public AbstractParseTreeVisitor()

Method Detail

visit

public T visit(ParseTree tree)

Visit a parse tree, and return a user-defined result of the operation.

The default implementation calls ParseTree.accept(org.antlr.v4.runtime.tree.ParseTreeVisitor<? extends T>) on the specified tree.

Specified by:

visit in interface ParseTreeVisitor<T>

Parameters:

tree - The ParseTree to visit.

Returns:

The result of visiting the parse tree.

visitChildren

public T visitChildren(RuleNode node)

Visit the children of a node, and return a user-defined result of the operation.

The default implementation initializes the aggregate result to defaultResult(). Before visiting each child, it calls shouldVisitNextChild; if the result is false no more children are visited and the current aggregate result is returned. After visiting a child, the aggregate result is updated by calling aggregateResult with the previous aggregate result and the result of visiting the child.

The default implementation is not safe for use in visitors that modify the tree structure. Visitors that modify the tree should override this method to behave properly in respect to the specific algorithm in use.

Specified by:

visitChildren in interface ParseTreeVisitor<T>

Parameters:

node - The RuleNode whose children should be visited.

Returns:

The result of visiting the children of the node.

visitTerminal

public T visitTerminal(TerminalNode node)

Visit a terminal node, and return a user-defined result of the operation.

The default implementation returns the result of defaultResult.

Specified by:

visitTerminal in interface ParseTreeVisitor<T>

Parameters:

node - The TerminalNode to visit.

Returns:

The result of visiting the node.

visitErrorNode

public T visitErrorNode(ErrorNode node)

Visit an error node, and return a user-defined result of the operation.

The default implementation returns the result of defaultResult.

Specified by:

visitErrorNode in interface ParseTreeVisitor<T>

Parameters:

node - The ErrorNode to visit.

Returns:

The result of visiting the node.

defaultResult

protected T defaultResult()

Gets the default value returned by visitor methods. This value is returned by the default implementations of visitTerminal, visitErrorNode. The default implementation of visitChildren initializes its aggregate result to this value.

The base implementation returns null.

Returns:

The default value returned by visitor methods.

aggregateResult

protected T aggregateResult(T aggregate,
                            T nextResult)

Aggregates the results of visiting multiple children of a node. After either all children are visited or shouldVisitNextChild(org.antlr.v4.runtime.tree.RuleNode, T) returns false, the aggregate value is returned as the result of visitChildren(org.antlr.v4.runtime.tree.RuleNode).

The default implementation returns nextResult, meaning visitChildren(org.antlr.v4.runtime.tree.RuleNode) will return the result of the last child visited (or return the initial value if the node has no children).

Parameters:

aggregate - The previous aggregate value. In the default implementation, the aggregate value is initialized to defaultResult(), which is passed as the aggregate argument to this method after the first child node is visited.

nextResult - The result of the immediately preceeding call to visit a child node.

Returns:

The updated aggregate result.

shouldVisitNextChild

protected boolean shouldVisitNextChild(RuleNode node,
                                       T currentResult)

This method is called after visiting each child in visitChildren(org.antlr.v4.runtime.tree.RuleNode). This method is first called before the first child is visited; at that point currentResult will be the initial value (in the default implementation, the initial value is returned by a call to defaultResult(). This method is not called after the last child is visited.

The default implementation always returns true, indicating that visitChildren should only return after all children are visited. One reason to override this method is to provide a "short circuit" evaluation option for situations where the result of visiting a single child has the potential to determine the result of the visit operation as a whole.

Parameters:

node - The RuleNode whose children are currently being visited.

currentResult - The current aggregate result of the children visited to the current point.

Returns:

true to continue visiting children. Otherwise return false to stop visiting children and immediately return the current aggregate result from visitChildren(org.antlr.v4.runtime.tree.RuleNode).