org.apache.xpath
Class Expression

java.lang.Object
  |
  +--org.apache.xpath.Expression
Direct Known Subclasses:
Function, NodeTest, Operation, UnaryOperation, UnionPattern, Variable, XObject

public abstract class Expression
extends java.lang.Object
implements java.io.Serializable, ExpressionNode, XPathVisitable

This abstract class serves as the base for all expression objects. An Expression can be executed to return a XObject, normally has a location within a document or DOM, can send error and warning events, and normally do not hold state and are meant to be immutable once construction has completed. An exception to the immutibility rule is iterators and walkers, which must be cloned in order to be used -- the original must still be immutable.

See Also:
Serialized Form

Constructor Summary
Expression()
           
 
Method Summary
 DTMIterator asIterator(XPathContext xctxt, int contextNode)
          Given an select expression and a context, evaluate the XPath and return the resulting iterator.
 DTMIterator asIteratorRaw(XPathContext xctxt, int contextNode)
          Given an select expression and a context, evaluate the XPath and return the resulting iterator, but do not clone.
 int asNode(XPathContext xctxt)
          Return the first node out of the nodeset, if this expression is a nodeset expression.
 void assertion(boolean b, java.lang.String msg)
          Tell the user of an assertion error, and probably throw an exception.
 boolean bool(XPathContext xctxt)
          Evaluate expression to a boolean.
 boolean canTraverseOutsideSubtree()
          Tell if this expression or it's subexpressions can traverse outside the current subtree.
abstract  boolean deepEquals(Expression expr)
          Compare this object with another object and see if they are equal, include the sub heararchy.
 void error(XPathContext xctxt, java.lang.String msg, java.lang.Object[] args)
          Tell the user of an error, and probably throw an exception.
abstract  XObject execute(XPathContext xctxt)
          Execute an expression in the XPath runtime context, and return the result of the expression.
 XObject execute(XPathContext xctxt, boolean destructiveOK)
          Execute an expression in the XPath runtime context, and return the result of the expression, but tell that a "safe" object doesn't have to be returned.
 XObject execute(XPathContext xctxt, int currentNode)
          Execute an expression in the XPath runtime context, and return the result of the expression.
 XObject execute(XPathContext xctxt, int currentNode, DTM dtm, int expType)
          Execute an expression in the XPath runtime context, and return the result of the expression.
 void executeCharsToContentHandler(XPathContext xctxt, ContentHandler handler)
          Execute an expression in the XPath runtime context, and return the result of the expression.
 void exprAddChild(ExpressionNode n, int i)
          This method tells the node to add its argument to the node's list of children.
 ExpressionNode exprGetChild(int i)
          This method returns a child node.
 int exprGetNumChildren()
          Return the number of children the node has.
 ExpressionNode exprGetParent()
           
 void exprSetParent(ExpressionNode n)
          This pair of methods are used to inform the node of its parent.
abstract  void fixupVariables(java.util.Vector vars, int globalsSize)
          This function is used to fixup variables from QNames to stack frame indexes at stylesheet build time.
 int getColumnNumber()
          Return the character position where the current document event ends.
 ExpressionNode getExpressionOwner()
          Get the first non-Expression parent of this node.
 int getLineNumber()
          Return the line number where the current document event ends.
 java.lang.String getPublicId()
          Return the public identifier for the current document event.
 java.lang.String getSystemId()
          Return the system identifier for the current document event.
 boolean isNodesetExpr()
          Tell if the expression is a nodeset expression.
 boolean isStableNumber()
          Tell if this expression returns a stable number that will not change during iterations within the expression.
 double num(XPathContext xctxt)
          Evaluate expression to a number.
 void warn(XPathContext xctxt, java.lang.String msg, java.lang.Object[] args)
          Warn the user of an problem.
 XMLString xstr(XPathContext xctxt)
          Cast result object to a string.
 
Methods inherited from class java.lang.Object
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

Expression

public Expression()
Method Detail

canTraverseOutsideSubtree

public boolean canTraverseOutsideSubtree()
Tell if this expression or it's subexpressions can traverse outside the current subtree.
Returns:
true if traversal outside the context node's subtree can occur.

execute

public XObject execute(XPathContext xctxt,
                       int currentNode)
                throws TransformerException
Execute an expression in the XPath runtime context, and return the result of the expression.
Parameters:
xctxt - The XPath runtime context.
currentNode - The currentNode.
Returns:
The result of the expression in the form of a XObject.
Throws:
TransformerException - if a runtime exception occurs.

execute

public XObject execute(XPathContext xctxt,
                       int currentNode,
                       DTM dtm,
                       int expType)
                throws TransformerException
Execute an expression in the XPath runtime context, and return the result of the expression.
Parameters:
xctxt - The XPath runtime context.
currentNode - The currentNode.
dtm - The DTM of the current node.
expType - The expanded type ID of the current node.
Returns:
The result of the expression in the form of a XObject.
Throws:
TransformerException - if a runtime exception occurs.

execute

public abstract XObject execute(XPathContext xctxt)
                         throws TransformerException
Execute an expression in the XPath runtime context, and return the result of the expression.
Parameters:
xctxt - The XPath runtime context.
Returns:
The result of the expression in the form of a XObject.
Throws:
TransformerException - if a runtime exception occurs.

execute

public XObject execute(XPathContext xctxt,
                       boolean destructiveOK)
                throws TransformerException
Execute an expression in the XPath runtime context, and return the result of the expression, but tell that a "safe" object doesn't have to be returned. The default implementation just calls execute(xctxt).
Parameters:
xctxt - The XPath runtime context.
destructiveOK - true if a "safe" object doesn't need to be returned.
Returns:
The result of the expression in the form of a XObject.
Throws:
TransformerException - if a runtime exception occurs.

num

public double num(XPathContext xctxt)
           throws TransformerException
Evaluate expression to a number.
Parameters:
xctxt - The XPath runtime context.
Returns:
The expression evaluated as a double.
Throws:
TransformerException -  

bool

public boolean bool(XPathContext xctxt)
             throws TransformerException
Evaluate expression to a boolean.
Parameters:
xctxt - The XPath runtime context.
Returns:
false
Throws:
TransformerException -  

xstr

public XMLString xstr(XPathContext xctxt)
               throws TransformerException
Cast result object to a string.
Parameters:
xctxt - The XPath runtime context.
Returns:
The string this wraps or the empty string if null
Throws:
TransformerException -  

isNodesetExpr

public boolean isNodesetExpr()
Tell if the expression is a nodeset expression. In other words, tell if you can execute asNode without an exception.
Returns:
true if the expression can be represented as a nodeset.

asNode

public int asNode(XPathContext xctxt)
           throws TransformerException
Return the first node out of the nodeset, if this expression is a nodeset expression.
Parameters:
xctxt - The XPath runtime context.
Returns:
the first node out of the nodeset, or DTM.NULL.
Throws:
TransformerException -  

asIterator

public DTMIterator asIterator(XPathContext xctxt,
                              int contextNode)
                       throws TransformerException
Given an select expression and a context, evaluate the XPath and return the resulting iterator.
Parameters:
xctxt - The execution context.
contextNode - The node that "." expresses.
Returns:
A valid DTMIterator.
Throws:
TransformerException - thrown if the active ProblemListener decides the error condition is severe enough to halt processing.
TransformerException -  
Usage:
**Experimental**

asIteratorRaw

public DTMIterator asIteratorRaw(XPathContext xctxt,
                                 int contextNode)
                          throws TransformerException
Given an select expression and a context, evaluate the XPath and return the resulting iterator, but do not clone.
Parameters:
xctxt - The execution context.
contextNode - The node that "." expresses.
Returns:
A valid DTMIterator.
Throws:
TransformerException - thrown if the active ProblemListener decides the error condition is severe enough to halt processing.
TransformerException -  
Usage:
**Experimental**

executeCharsToContentHandler

public void executeCharsToContentHandler(XPathContext xctxt,
                                         ContentHandler handler)
                                  throws TransformerException,
                                         SAXException
Execute an expression in the XPath runtime context, and return the result of the expression.
Parameters:
xctxt - The XPath runtime context. NEEDSDOC @param handler
Returns:
The result of the expression in the form of a XObject.
Throws:
TransformerException - if a runtime exception occurs.
SAXException -  

isStableNumber

public boolean isStableNumber()
Tell if this expression returns a stable number that will not change during iterations within the expression. This is used to determine if a proximity position predicate can indicate that no more searching has to occur.
Returns:
true if the expression represents a stable number.

fixupVariables

public abstract void fixupVariables(java.util.Vector vars,
                                    int globalsSize)
This function is used to fixup variables from QNames to stack frame indexes at stylesheet build time.
Parameters:
vars - List of QNames that correspond to variables. This list should be searched backwards for the first qualified name that corresponds to the variable reference qname. The position of the QName in the vector from the start of the vector will be its position in the stack frame (but variables above the globalsTop value will need to be offset to the current stack frame). NEEDSDOC @param globalsSize

deepEquals

public abstract boolean deepEquals(Expression expr)
Compare this object with another object and see if they are equal, include the sub heararchy.
Parameters:
expr - Another expression object.
Returns:
true if this objects class and the expr object's class are the same, and the data contained within both objects are considered equal.

warn

public void warn(XPathContext xctxt,
                 java.lang.String msg,
                 java.lang.Object[] args)
          throws TransformerException
Warn the user of an problem.
Parameters:
xctxt - The XPath runtime context.
msg - An error msgkey that corresponds to one of the conststants found in XPATHErrorResources, which is a key for a format string.
args - An array of arguments represented in the format string, which may be null.
Throws:
TransformerException - if the current ErrorListoner determines to throw an exception.
TransformerException -  

assertion

public void assertion(boolean b,
                      java.lang.String msg)
Tell the user of an assertion error, and probably throw an exception.
Parameters:
b - If false, a runtime exception will be thrown.
msg - The assertion message, which should be informative.
Throws:
java.lang.RuntimeException - if the b argument is false.
TransformerException -  

error

public void error(XPathContext xctxt,
                  java.lang.String msg,
                  java.lang.Object[] args)
           throws TransformerException
Tell the user of an error, and probably throw an exception.
Parameters:
xctxt - The XPath runtime context.
msg - An error msgkey that corresponds to one of the constants found in XPATHErrorResources, which is a key for a format string.
args - An array of arguments represented in the format string, which may be null.
Throws:
TransformerException - if the current ErrorListoner determines to throw an exception.
TransformerException -  

getExpressionOwner

public ExpressionNode getExpressionOwner()
Get the first non-Expression parent of this node.
Returns:
null or first ancestor that is not an Expression.

exprSetParent

public void exprSetParent(ExpressionNode n)
This pair of methods are used to inform the node of its parent.
Specified by:
exprSetParent in interface ExpressionNode

exprGetParent

public ExpressionNode exprGetParent()
Specified by:
exprGetParent in interface ExpressionNode

exprAddChild

public void exprAddChild(ExpressionNode n,
                         int i)
This method tells the node to add its argument to the node's list of children.
Specified by:
exprAddChild in interface ExpressionNode

exprGetChild

public ExpressionNode exprGetChild(int i)
This method returns a child node. The children are numbered from zero, left to right.
Specified by:
exprGetChild in interface ExpressionNode

exprGetNumChildren

public int exprGetNumChildren()
Return the number of children the node has.
Specified by:
exprGetNumChildren in interface ExpressionNode

getPublicId

public java.lang.String getPublicId()
Return the public identifier for the current document event.

The return value is the public identifier of the document entity or of the external parsed entity in which the markup that triggered the event appears.

Returns:
A string containing the public identifier, or null if none is available.
See Also:
getSystemId()

getSystemId

public java.lang.String getSystemId()
Return the system identifier for the current document event.

The return value is the system identifier of the document entity or of the external parsed entity in which the markup that triggered the event appears.

If the system identifier is a URL, the parser must resolve it fully before passing it to the application.

Returns:
A string containing the system identifier, or null if none is available.
See Also:
getPublicId()

getLineNumber

public int getLineNumber()
Return the line number where the current document event ends.

Warning: The return value from the method is intended only as an approximation for the sake of error reporting; it is not intended to provide sufficient information to edit the character content of the original XML document.

The return value is an approximation of the line number in the document entity or external parsed entity where the markup that triggered the event appears.

Returns:
The line number, or -1 if none is available.
See Also:
getColumnNumber()

getColumnNumber

public int getColumnNumber()
Return the character position where the current document event ends.

Warning: The return value from the method is intended only as an approximation for the sake of error reporting; it is not intended to provide sufficient information to edit the character content of the original XML document.

The return value is an approximation of the column number in the document entity or external parsed entity where the markup that triggered the event appears.

Returns:
The column number, or -1 if none is available.
See Also:
getLineNumber()


Copyright 2006 Apache XML Project. All Rights Reserved.