org.apache.xpath
Class VariableStack

java.lang.Object
  org.apache.xpath.VariableStack

All Implemented Interfaces:

Cloneable

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.

Field Summary

private int	_currentFrameBottom The bottom index of the current frame (relative to _stackFrames).
(package private) int	_frameTop The top of the stack frame (_stackFrames).
(package private) int[]	_links The stack of frame positions.
(package private) int	_linksTop The top of the links stack.
(package private) XObject[]	_stackFrames The stack frame where all variables and params will be kept.
private static XObject[]	m_nulls NEEDSDOC Field m_nulls

Constructor Summary

VariableStack()
Constructor for a variable stack.

Method Summary

void	clearLocalSlots(int start, int len) Use this to clear the variables in a section of the stack.
Object	clone() Returns a clone of this variable stack.
XObject	elementAt(int i) Get the element at the given index, regardless of stackframe.
XObject	getGlobalVariable(XPathContext xctxt, int index) Get a global variable or parameter from the global stack frame.
XObject	getGlobalVariable(XPathContext xctxt, int index, boolean destructiveOK) Get a global variable or parameter from the global stack frame.
XObject	getLocalVariable(int index, int frame) Get a local variable or parameter in the current stack frame.
XObject	getLocalVariable(XPathContext xctxt, int index) Get a local variable or parameter in the current stack frame.
XObject	getLocalVariable(XPathContext xctxt, int index, boolean destructiveOK) Get a local variable or parameter in the current stack frame.
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.
XObject	getVariableOrParam(XPathContext xctxt, QName qname) Get a variable based on it's qualified name.
boolean	isLocalSet(int index) Tell if a local variable has been set or not.
int	link(int size) Allocates memory (called a stackframe) on the stack; used to store local variables and parameter arguments.
void	reset() Reset the stack to a start position.
void	setGlobalVariable(int index, XObject val) Set a global variable or parameter in the global stack frame.
void	setLocalVariable(int index, XObject val) Set a local variable or parameter in the current stack frame.
void	setLocalVariable(int index, XObject val, int stackFrame) Set a local variable or parameter in the specified stack frame.
void	setStackFrame(int sf) Set the current stack frame.
int	size() Get size of the stack.
void	unlink() Free up the stack frame that was last allocated with link(int size).
void	unlink(int currentFrame) Free up the stack frame that was last allocated with link(int size).

Methods inherited from class java.lang.Object

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

Field Detail

_stackFrames

XObject[] _stackFrames

The stack frame where all variables and params will be kept.

_frameTop

int _frameTop

The top of the stack frame (_stackFrames).

_currentFrameBottom

private int _currentFrameBottom

The bottom index of the current frame (relative to _stackFrames).

_links

int[] _links

The stack of frame positions. I call 'em links because of distant Motorola 68000 assembler memories. :-)

_linksTop

int _linksTop

The top of the links stack.

m_nulls

private static XObject[] m_nulls

NEEDSDOC Field m_nulls

Constructor Detail

VariableStack

public VariableStack()

Constructor for a variable stack.

Method Detail

clone

public Object clone()
             throws CloneNotSupportedException

Returns a clone of this variable stack.

Overrides:

clone in class Object

Returns:

a clone of this variable stack.

Throws:

CloneNotSupportedException

See Also:

Cloneable

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.

size

public int size()

Get size of the stack.

Returns:

the total size of the execution stack.

reset

public void reset()

Reset the stack to a start position.

Returns:

the total size of the execution stack.

setStackFrame

public void setStackFrame(int sf)

Set the current stack frame.

Parameters:

sf - The new stack frame position.

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.

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.

unlink

public void unlink()

Free up the stack frame that was last allocated with link(int size).

unlink

public void unlink(int currentFrame)

Free up the stack frame that was last allocated with link(int size).

Parameters:

currentFrame - The current frame to set to after the unlink.

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.

getLocalVariable

public XObject getLocalVariable(XPathContext xctxt,
                                int index)
                         throws javax.xml.transform.TransformerException

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:

javax.xml.transform.TransformerException

getLocalVariable

public XObject getLocalVariable(int index,
                                int frame)
                         throws javax.xml.transform.TransformerException

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:

javax.xml.transform.TransformerException

getLocalVariable

public XObject getLocalVariable(XPathContext xctxt,
                                int index,
                                boolean destructiveOK)
                         throws javax.xml.transform.TransformerException

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:

javax.xml.transform.TransformerException

isLocalSet

public boolean isLocalSet(int index)
                   throws javax.xml.transform.TransformerException

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:

javax.xml.transform.TransformerException

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.

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.

getGlobalVariable

public XObject getGlobalVariable(XPathContext xctxt,
                                 int index)
                          throws javax.xml.transform.TransformerException

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:

javax.xml.transform.TransformerException

getGlobalVariable

public XObject getGlobalVariable(XPathContext xctxt,
                                 int index,
                                 boolean destructiveOK)
                          throws javax.xml.transform.TransformerException

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:

javax.xml.transform.TransformerException

getVariableOrParam

public XObject getVariableOrParam(XPathContext xctxt,
                                  QName qname)
                           throws javax.xml.transform.TransformerException

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