org.apache.xpath
Class VariableStack

java.lang.Object
  |
  +--org.apache.xpath.VariableStack
Direct Known Subclasses:
JAXPVariableStack

public class VariableStack
extends java.lang.Object
implements java.lang.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.

Usage:
**For internal use only**

Field Summary
static int CLEARLIMITATION
          limitation for 1K
 
Constructor Summary
VariableStack()
          Constructor for a variable stack.
VariableStack(int initStackSize)
          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.
 java.lang.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, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

CLEARLIMITATION

public static final int CLEARLIMITATION
limitation for 1K
Constructor Detail

VariableStack

public VariableStack()
Constructor for a variable stack.

VariableStack

public VariableStack(int initStackSize)
Constructor for a variable stack.
Parameters:
initStackSize - The initial stack size. Must be at least one. The stack can grow if needed.
Method Detail

clone

public java.lang.Object clone()
                       throws java.lang.CloneNotSupportedException
Returns a clone of this variable stack.
Returns:
a clone of this variable stack.
Throws:
java.lang.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.

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.

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 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:
TransformerException -  

getLocalVariable

public XObject getLocalVariable(int index,
                                int frame)
                         throws 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:
TransformerException -  

getLocalVariable

public XObject getLocalVariable(XPathContext xctxt,
                                int index,
                                boolean destructiveOK)
                         throws 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:
TransformerException -  

isLocalSet

public boolean isLocalSet(int index)
                   throws 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:
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 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:
TransformerException -  

getGlobalVariable

public XObject getGlobalVariable(XPathContext xctxt,
                                 int index,
                                 boolean destructiveOK)
                          throws 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:
TransformerException -  

getVariableOrParam

public XObject getVariableOrParam(XPathContext xctxt,
                                  QName qname)
                           throws 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:
TransformerException -  


Copyright 2006 Apache XML Project. All Rights Reserved.