Package com.singularsys.extensions.xjep

Class XAssign

java.lang.Object

com.singularsys.jep.functions.PostfixMathCommand

com.singularsys.extensions.xjep.XAssign

All Implemented Interfaces:

CommandVisitorI, CallbackEvaluationI, JepComponent, PostfixMathCommandI, java.io.Serializable

public class XAssign
extends PostfixMathCommand
implements CallbackEvaluationI, CommandVisitorI, JepComponent

An assignment operator which implements the CommandVisitorI interface. When process is called the equation of the variable on the LHS is set to the RHS.

Author:

Rich Morris Created on 18-Nov-2003

See Also:

Serialized Form

Field Summary

Fields inherited from class com.singularsys.jep.functions.PostfixMathCommand

curNumberOfParameters, name, NaN, numberOfParameters

Constructor Summary

Constructors

Constructor	Description
XAssign()	Constructor using Assign for the basic evaluation method.
XAssign(boolean useEqn)	Constructor to suppress copying of equations.
XAssign(XJep jep, boolean b)
XAssign(CallbackEvaluationI root)	Decorator constructor using a specified function for evaluation.

Method Summary

Modifier and Type	Method	Description
java.lang.Object	evaluate(Node node, Evaluator pv)	Performs some special evaluation on the node.
JepComponent	getLightWeightInstance()	Gets a light-weight instance suitable for using in multiple threads.
void	init(Jep jep)	Initialize the component.
boolean	isUseEquation()	Whether equations are used.
Node	process(Node node, Node[] children)	In the pre-process stage, set the equation of the lhs variable to the rhs equation.
void	run(java.util.Stack<java.lang.Object> aStack)	Throws an exception because this method should never be called under normal circumstances.

Methods inherited from class com.singularsys.jep.functions.PostfixMathCommand

asArray, asBool, asDouble, asInt, asLong, asStrictInt, asString, checkNumberOfParameters, getName, getNumberOfParameters, setCurNumberOfParameters, setName, toString, toString

Methods inherited from class java.lang.Object

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

Constructor Detail

XAssign

public XAssign()

Constructor using Assign for the basic evaluation method.

XAssign

public XAssign(boolean useEqn)

Constructor to suppress copying of equations. Used when two different assignment operators are used, one for symbolic assignment and one which is only used for evaluation.

Parameters:

useEqn - if false equations are never set

XAssign

public XAssign(CallbackEvaluationI root)

Decorator constructor using a specified function for evaluation.

Parameters:

root - function used for evaluation

XAssign

public XAssign(XJep jep,
               boolean b)

Method Detail

process

public Node process(Node node,
                    Node[] children)
             throws ParseException

In the pre-process stage, set the equation of the lhs variable to the rhs equation. If the useEqn flag is set in XAssign(boolean) then the rhigh hand side is preprocessed, but no action is taken on the lhs. If useEqn is true then if the lhs implements SymbolicLValueI calls SymbolicLValueI.setEqn(Jep, Node, Node).

Specified by:

process in interface CommandVisitorI

Parameters:

node - top node of the tree

children - the children of the node after they have been preprocessed.

Returns:

top node of the results.

Throws:

ParseException - if lhs is neither a variable or an LValue.

evaluate

public java.lang.Object evaluate(Node node,
                                 Evaluator pv)
                          throws EvaluationException

Description copied from interface: CallbackEvaluationI

Performs some special evaluation on the node. This method has the responsibility for evaluating the children of the node and it should generally call

 pv.eval(node.jjtGetChild(i))   
 

for each child. The SymbolTable is not passed as an argument. This is because it is better practice to get and set variable values by using node.getVar().setValue() rather that through the SymbolTable with requires a hashtable lookup.

Specified by:

evaluate in interface CallbackEvaluationI

Parameters:

node - The current node

pv - The visitor, can be used evaluate the children

Returns:

the value after evaluation. This value will be passed to other functions higher up the node tree. The value can be any type including Double or Vector<Object>

Throws:

EvaluationException - if the calculation cannot be performed

See Also:

Evaluator

run

public void run(java.util.Stack<java.lang.Object> aStack)
         throws EvaluationException

Description copied from class: PostfixMathCommand

Throws an exception because this method should never be called under normal circumstances. Each function should use it's own run() method for evaluating the function. This includes popping off the parameters from the stack, and pushing the result back on the stack.

Specified by:

run in interface PostfixMathCommandI

Overrides:

run in class PostfixMathCommand

Parameters:

aStack - arguments for function

Throws:

EvaluationException - if function cannot be evaluated

isUseEquation

public boolean isUseEquation()

Whether equations are used.

Returns:

init

public void init(Jep jep)

Description copied from interface: JepComponent

Initialize the component. This methods is called whenever a component is added to Jep. Hence it allows components to keep track of the other components they may rely on.

Specified by:

init in interface JepComponent

Parameters:

jep - the current Jep instance

getLightWeightInstance

public JepComponent getLightWeightInstance()

Description copied from interface: JepComponent

Gets a light-weight instance suitable for using in multiple threads.

Specified by:

getLightWeightInstance in interface JepComponent

Returns:

either an new instance, null or 'this'.