org.apache.xpath

Class VariableStack

public class VariableStack extends Object implements Cloneable

Defines a class to keep track of a stack for template arguments and variables.

This has been changed from the previous incarnations of this class to be fairly low level.

UNKNOWN: internal

Field Summary
static intCLEARLIMITATION
limitation for 1K
Constructor Summary
VariableStack()
Constructor for a variable stack.
Method Summary
voidclearLocalSlots(int start, int len)
Use this to clear the variables in a section of the stack.
Objectclone()
Returns a clone of this variable stack.
XObjectelementAt(int i)
Get the element at the given index, regardless of stackframe.
XObjectgetGlobalVariable(XPathContext xctxt, int index)
Get a global variable or parameter from the global stack frame.
XObjectgetGlobalVariable(XPathContext xctxt, int index, boolean destructiveOK)
Get a global variable or parameter from the global stack frame.
XObjectgetLocalVariable(XPathContext xctxt, int index)
Get a local variable or parameter in the current stack frame.
XObjectgetLocalVariable(int index, int frame)
Get a local variable or parameter in the current stack frame.
XObjectgetLocalVariable(XPathContext xctxt, int index, boolean destructiveOK)
Get a local variable or parameter in the current stack frame.
intgetStackFrame()
Get the position from where the search should start, which is either the searchStart property, or the top of the stack if that value is -1.
XObjectgetVariableOrParam(XPathContext xctxt, QName qname)
Get a variable based on it's qualified name.
booleanisLocalSet(int index)
Tell if a local variable has been set or not.
intlink(int size)
Allocates memory (called a stackframe) on the stack; used to store local variables and parameter arguments.
voidreset()
Reset the stack to a start position.
voidsetGlobalVariable(int index, XObject val)
Set a global variable or parameter in the global stack frame.
voidsetLocalVariable(int index, XObject val)
Set a local variable or parameter in the current stack frame.
voidsetLocalVariable(int index, XObject val, int stackFrame)
Set a local variable or parameter in the specified stack frame.
voidsetStackFrame(int sf)
Set the current stack frame.
intsize()
Get size of the stack.
voidunlink()
Free up the stack frame that was last allocated with VariableStack.
voidunlink(int currentFrame)
Free up the stack frame that was last allocated with VariableStack.

Field Detail

CLEARLIMITATION

public static final int CLEARLIMITATION
limitation for 1K

Constructor Detail

VariableStack

public VariableStack()
Constructor for a variable stack.

Method Detail

clearLocalSlots

public void clearLocalSlots(int start, int len)
Use this to clear the variables in a section of the stack. This is used to clear the parameter section of the stack, so that default param values can tell if they've already been set. It is important to note that this function has a 1K limitation.

Parameters: start The start position, relative to the current local stack frame. len The number of slots to be cleared.

clone

public Object clone()
Returns a clone of this variable stack.

Returns: a clone of this variable stack.

Throws: CloneNotSupportedException

elementAt

public XObject elementAt(int i)
Get the element at the given index, regardless of stackframe.

Parameters: i index from zero.

Returns: The item at the given index.

getGlobalVariable

public XObject getGlobalVariable(XPathContext xctxt, int index)
Get a global variable or parameter from the global stack frame.

Parameters: xctxt The XPath context, which must be passed in order to lazy evaluate variables. index Global variable index relative to the global stack frame bottom.

Returns: The value of the variable.

Throws: TransformerException

getGlobalVariable

public XObject getGlobalVariable(XPathContext xctxt, int index, boolean destructiveOK)
Get a global variable or parameter from the global stack frame.

Parameters: xctxt The XPath context, which must be passed in order to lazy evaluate variables. index Global variable index relative to the global stack frame bottom.

Returns: The value of the variable.

Throws: TransformerException

getLocalVariable

public XObject getLocalVariable(XPathContext xctxt, int index)
Get a local variable or parameter in the current stack frame.

Parameters: xctxt The XPath context, which must be passed in order to lazy evaluate variables. index Local variable index relative to the current stack frame bottom.

Returns: The value of the variable.

Throws: TransformerException

getLocalVariable

public XObject getLocalVariable(int index, int frame)
Get a local variable or parameter in the current stack frame.

Parameters: index Local variable index relative to the given frame bottom. NEEDSDOC @param frame

Returns: The value of the variable.

Throws: TransformerException

getLocalVariable

public XObject getLocalVariable(XPathContext xctxt, int index, boolean destructiveOK)
Get a local variable or parameter in the current stack frame.

Parameters: xctxt The XPath context, which must be passed in order to lazy evaluate variables. index Local variable index relative to the current stack frame bottom.

Returns: The value of the variable.

Throws: TransformerException

getStackFrame

public int getStackFrame()
Get the position from where the search should start, which is either the searchStart property, or the top of the stack if that value is -1.

Returns: The current stack frame position.

getVariableOrParam

public XObject getVariableOrParam(XPathContext xctxt, QName qname)
Get a variable based on it's qualified name. This is for external use only.

Parameters: xctxt The XPath context, which must be passed in order to lazy evaluate variables. qname The qualified name of the variable.

Returns: The evaluated value of the variable.

Throws: javax.xml.transform.TransformerException

isLocalSet

public boolean isLocalSet(int index)
Tell if a local variable has been set or not.

Parameters: index Local variable index relative to the current stack frame bottom.

Returns: true if the value at the index is not null.

Throws: TransformerException

link

public int link(int size)
Allocates memory (called a stackframe) on the stack; used to store local variables and parameter arguments.

I use the link/unlink concept because of distant Motorola 68000 assembler memories.

Parameters: size The size of the stack frame allocation. This ammount should normally be the maximum number of variables that you can have allocated at one time in the new stack frame.

Returns: The bottom of the stack frame, from where local variable addressing should start from.

reset

public void reset()
Reset the stack to a start position.

Returns: the total size of the execution stack.

setGlobalVariable

public void setGlobalVariable(int index, XObject val)
Set a global variable or parameter in the global stack frame.

Parameters: index Local variable index relative to the global stack frame bottom. val The value of the variable that is being set.

setLocalVariable

public void setLocalVariable(int index, XObject val)
Set a local variable or parameter in the current stack frame.

Parameters: index Local variable index relative to the current stack frame bottom. val The value of the variable that is being set.

setLocalVariable

public void setLocalVariable(int index, XObject val, int stackFrame)
Set a local variable or parameter in the specified stack frame.

Parameters: index Local variable index relative to the current stack frame bottom. NEEDSDOC @param stackFrame val The value of the variable that is being set.

setStackFrame

public void setStackFrame(int sf)
Set the current stack frame.

Parameters: sf The new stack frame position.

size

public int size()
Get size of the stack.

Returns: the total size of the execution stack.

unlink

public void unlink()
Free up the stack frame that was last allocated with VariableStack.

unlink

public void unlink(int currentFrame)
Free up the stack frame that was last allocated with VariableStack.

Parameters: currentFrame The current frame to set to after the unlink.

Copyright B) 2005 Apache XML Project. All Rights Reserved.