Package gnu.jel

Class Evaluator

java.lang.Object
gnu.jel.Evaluator
public class Evaluator
extends java.lang.Object
This is the main frontend to JEL.

It is intended for compilation of algebraic expressions involving functions.

Syntax allows variables, which can be either a public fields of certain objects or functions with no arguments. If a method like "double x() {};" is defined in the dynamic library class (see gnu.jel.Library documentation on how to do this), an expression "sin(x)" will call the method "x()" ( and function Math.sin() ) each time it is evaluated. Static methods in namespace are assumed to be stateless (unless this default behaviour is explicitly overridden, as is necessary for Math.random()) and will be called at compile time if their arguments are known.

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 compiler can do all the type conversions permissible in Java language and more (e.g. between reflection wrappers java.lang.Integer,... and primitives). Widening type conversions (not leading to precision loss) are applied by JEL automatically, narrowing should be explicitly requested.

There is variant of the "compile" function with three arguments, which allows to fix the type of the expression result. For example: 

 CompiledExpression expression=compile("2*6+6",lib,Double.TYPE);
will produce a 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 unexpected return types.

(c) 1998-2003, by Konstantin Metlov
Prague, CZ

See Also:
CompiledExpression, Library

  • Field Summary

    Fields 
    Modifier and Type Field Description
    protected static ClassFile cf_orig  
    protected static LocalMethod[] eval_methods  
    protected static int retID_patchback  
    protected static int retIDC_patchback  

  • Constructor Summary

    Constructors 
    Constructor Description
    Evaluator()  

  • Method Summary

    Modifier and Type Method Description
    static CompiledExpression compile​(java.lang.String expression, Library lib)
    Compiles expression, resolving the function names in the library.
    static CompiledExpression compile​(java.lang.String expression, Library lib, java.lang.Class<?> resultType)
    Compiles expression, resolving the function names in the library.
    static byte[] compileBits​(java.lang.String expression, Library lib)
    Compiles expression, resolving the function names in the library.
    static byte[] compileBits​(java.lang.String expression, Library lib, java.lang.Class<?> resultType)
    Compiles expression, resolving the function names in the library.

    Methods inherited from class java.lang.Object

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

  • Field Details

  • Constructor Details

  • Method Details

    • compile

      public static CompiledExpression compile​(java.lang.String expression, Library lib, java.lang.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:
      CompiledExpression

    • compileBits

      public static byte[] compileBits​(java.lang.String expression, Library lib, java.lang.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:
      Byte array, representing the expression in a standard Java classfile format. It can be conveniently loaded (with renaming, if necessary) into Java VM using gnu.jel.ImageLoader.
      Throws:
      CompilationException - if the expression is not syntactically or semantically correct.
      See Also:
      CompiledExpression, ImageLoader

    • compile

      public static CompiledExpression compile​(java.lang.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:
      CompiledExpression

    • compileBits

      public static byte[] compileBits​(java.lang.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:
      Byte array, representing the expression in a standard Java classfile format. It can be conveniently loaded (with renaming, if necessary) into Java VM using gnu.jel.ImageLoader.
      Throws:
      CompilationException - if the expression is not syntactically or semantically correct.
      See Also:
      CompiledExpression, ImageLoader