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Class gnu.jel.Evaluator

java.lang.Object
   |
   +----gnu.jel.Evaluator

public class Evaluator
extends Object
This is the main front end to JEL.

It is intended for compilation of algebraic expressions, involving functions.

Syntax supports variables, which are, in fact, functions with no arguments. If You define such function in the static library -- it is a constant (and will be substituted into expression at compile time). If you define the method , such as "double x() {};" in the dynamic library class the expression "sin(x)" will call the method "x()" ( and function Math.sin() ) each time it is evaluated.

It is possible to have any type of intermediate object throughout the calculation as long as types of the function return values and parameters stay compatible.

The variant of the "compile" function with three arguments allows to fix the type of the expression result. For example :

 CompiledExpression expression=compile("2*6+6",lib,Double.TYPE);
 
will produce compiled expression, whose return type is always double. For additional information on how to use this feature to eliminate object allocation overhead see gnu.jel.CompiledExpression documentation.

Care should be taken during the assembly of static and dynamic libraries to avoid conflicts and unsupported return types.

(c) 1998, by Konstantin Metlov
Prague, CZ

See Also:
CompiledExpression

Constructor Index

 o Evaluator()

Method Index

 o compile(String, Library)
Compiles expression, resolving the function names in the library.
 o compile(String, Library, Class)
Compiles expression, resolving the function names in the library.
 o compileBits(String, Library)
Compiles expression, resolving the function names in the library.
 o compileBits(String, Library, Class)
Compiles expression, resolving the function names in the library.

Constructors

 o Evaluator
 public Evaluator()

Methods

 o compile
 public static CompiledExpression compile(String expression,
                                          Library lib,
                                          Class resultType) throws CompilationException
Compiles expression, resolving the function names in the library.

Parameters:
expression - is the expression to compile. i.e. "sin(666)" .
lib - Library of functions exported for use in expression.
resultType - identifies the type result should be converted to. Can be null, in this case the result type is not fixed.
Returns:
Instance of the CompiledExpression subclass, implementing the specified expression evaluation.
Throws: CompilationException
if the expression is not syntactically or semantically correct.
See Also:
evaluate
 o compileBits
 public static ExpressionBits compileBits(String expression,
                                          Library lib,
                                          Class resultType) throws CompilationException
Compiles expression, resolving the function names in the library.

This variant of compile allows to store expressions in a java.io.OutputStream using Java serialization mechanism.

Parameters:
expression - is the expression to compile. i.e. "sin(666)" .
lib - Library of functions exported for use in expression.
resultType - identifies the type result should be converted to. Can be null, in this case the result type is not fixed.
Returns:
Instance of the ExpressionBits class, allowing to store and/or instantiate compiled expression.
Throws: CompilationException
if the expression is not syntactically or semantically correct.
See Also:
evaluate
 o compile
 public static CompiledExpression compile(String expression,
                                          Library lib) throws CompilationException
Compiles expression, resolving the function names in the library.

Parameters:
expression - is the expression to compile. i.e. "sin(666)" .
lib - Library of functions exported for use in expression.
Returns:
Instance of the CompiledExpression subclass, implementing the specified expression evaluation.
Throws: CompilationException
if the expression is not syntactically or semantically correct.
See Also:
evaluate
 o compileBits
 public static ExpressionBits compileBits(String expression,
                                          Library lib) throws CompilationException
Compiles expression, resolving the function names in the library.

This variant of compile allows to store expressions in a java.io.OutputStream using Java serialization mechanism.

Parameters:
expression - is the expression to compile. i.e. "sin(666)" .
lib - Library of functions exported for use in expression.
Returns:
Instance of the ExpressionBits class, allowing to store and/or instantiate compiled expression.
Throws: CompilationException
if the expression is not syntactically or semantically correct.
See Also:
evaluate

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