gnu.jel
Class CompiledExpression

java.lang.Object
  extended by gnu.jel.CompiledExpression

public abstract class CompiledExpression
extends Object

This abstract class is a superclass of every JEL-compiled expression, each of which overrides some of the abstract methods below.

Most methods of this class accept a reference to the array of objects. This reference is a pointer to the dynamic object library. As you know, JEL allows to call virtual methods of Java classes, but, as you also know, virtual methods require a reference to an object instance (this) to be passed along with parameters. The array dl (dynamic library) serves just this purpose. It should contain references to objects of all classes, whose virtual methods were put into the Library of callable functions. Objects in the dl array should correspond one-to-one to classes in the array, passed as a second argument of gnu.jel.Library constructor.

There are two ways of evaluating the compiled expressions allowing to compromise between raw performance and simplicity:

The first method (simplest one) is based on the call to the evaluate method, which will return an object even if the result of computation was of a primitive type. The primitive types will be automatically converted into the corresponding reflection objects. There is certain overhead, associated with object creation, it takes CPU cycles and also produces load on the garbage collector later..

For massive (thousand times) evaluations of functions, producing results of primitive Java types, the second method can be more suitable. It is based on : first, determining the type of the result, and, then, subsequent call to the corresponding evaluateXXX method.

The type of the resulting expression can be determined by call to the getType() method. It will return an integer number, indentifying the type, proper evaluateXXX method can be determined, based on the following table:

 getType()   |  method to call
 ------------+----------------------
 0           | evaluate_boolean(...)
 1           | evaluate_byte(...)
 2           | evaluate_char(...)
 3           | evaluate_short(...)
 4           | evaluate_int(...)
 5           | evaluate_long(...)
 6           | evaluate_float(...)
 7           | evaluate_double(...)
 8           | evaluate(...)         <- result is Object (universal method)
 9           | evaluate_void(...)
 -----------------------------------
 

Note: If a wrong evaluateXXX() method is called, it will return zero, and, in debug version of JEL (jel_g.jar) only, a warning will be printed to stderr.

There is a possibility to enforce resulting type of the expression at compile time (see gnu.jel.Evaluator). Use it to avoid unnecesary type checks.

See Also:
Library, Evaluator

Constructor Summary
CompiledExpression()
           
 
Method Summary
static int compare(String s1, String s2)
           
 boolean evaluate_boolean(Object[] dl)
          Evaluates the expression whose result has type boolean.
 byte evaluate_byte(Object[] dl)
          Evaluates the expression whose result has type byte.
 char evaluate_char(Object[] dl)
          Evaluates the expression whose result has type char.
 double evaluate_double(Object[] dl)
          Evaluates the expression whose result has type double.
 float evaluate_float(Object[] dl)
          Evaluates the expression whose result has type float.
 int evaluate_int(Object[] dl)
          Evaluates the expression whose result has type int.
 long evaluate_long(Object[] dl)
          Evaluates the expression whose result has type long.
 short evaluate_short(Object[] dl)
          Evaluates the expression whose result has type short.
 void evaluate_void(Object[] dl)
          Evaluates the expression whose result has type void.
 Object evaluate(Object[] dl)
          Evaluates the expression, representing result as an object.
abstract  int getType()
          Returns type of the expression result.
abstract  Class getTypeC()
          Returns the type of the expression result.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

CompiledExpression

public CompiledExpression()
Method Detail

getType

public abstract int getType()
Returns type of the expression result.

The type is encoded in integer. Following table could help in determining what it is :

 getType()   |  method to call
 ------------+-----------------
 0           | boolean
 1           | byte
 2           | char
 3           | short
 4           | int
 5           | long
 6           | float
 7           | double
 8           | Object
 9           | void
 

The reason not to introduce the family of, say, TYPE_XXX constants is to save space. There are so many things connected with these particular numbers in code generator that it could be a pain to change their meaning. Also, this shoul never be necessary because these are ALL Java 1.X primitive types.

Returns:
the type of the expression, encoded in integer.

getTypeC

public abstract Class getTypeC()
Returns the type of the expression result.

If the result has primitive type the corresponding wrapper class is returned (please note that it is just a wrapper class like java.lang.Integer instead of exact primitive type class java.lang.Integer.TYPE). This corresponds to the wrapping done in non-specialized evaluate() method.

When the result is an object, the returned value is the most specific reference to the class of that object (which is always a subclass of the returned class) available at compile time.

The precision of determining the result type this way mainly depends on the design of the user's function namespace (defined by gnu.jel.Library class). It is possible to design a library in such a way that the best approximation to the result type obtainable at compile time would be the java.lang.Object class, which will be returned by this method, thus, providing no useful information about the actual type.

Please note again that the guaranteed exact type of the result can't be determined at compile time and can be quiered only after evaluating the expression (directly from resulting object).

The only guarantee this method provides is that a variable of the returned expression type can be assigned by a reference, resulting from a call to evaluate.


evaluate

public Object evaluate(Object[] dl)
                throws Throwable
Evaluates the expression, representing result as an object.

If the result of evaluation is Java primitive type it gets wrapped into corresponding reflection object , i.e. int -> java.lang.Integer, boolean -> java.lang.Boolean,...

Parameters:
dl - Array of the instance references to the objects in dynamic library. See description of this class above for more details.
Returns:
the result fo computation.
Throws:
Throwable - if any runtime error have occured (i.e. division by 0)
See Also:
Evaluator.compile(java.lang.String, gnu.jel.Library, java.lang.Class), Library

evaluate_boolean

public boolean evaluate_boolean(Object[] dl)
                         throws Throwable
Evaluates the expression whose result has type boolean.

If the type of the result is not a boolean this function returns always false, debug version will print a warning to stderr.

Parameters:
dl - Array of the instance references to the objects in dynamic library. See description of this class above for more details.
Returns:
the result fo computation.
Throws:
Throwable - if any runtime error have occured (i.e. division by 0)
See Also:
Evaluator.compile(java.lang.String, gnu.jel.Library, java.lang.Class), Library

evaluate_byte

public byte evaluate_byte(Object[] dl)
                   throws Throwable
Evaluates the expression whose result has type byte.

If the type of the result is not a byte this function returns always 0, debug version will print a warning to stderr.

Parameters:
dl - Array of the instance references to the objects in dynamic library. See description of this class above for more details.
Returns:
the result fo computation.
Throws:
Throwable - if any runtime error have occured (i.e. division by 0)
See Also:
Evaluator.compile(java.lang.String, gnu.jel.Library, java.lang.Class), Library

evaluate_short

public short evaluate_short(Object[] dl)
                     throws Throwable
Evaluates the expression whose result has type short.

If the type of the result is not a short this function returns always 0, debug version will print a warning to stderr.

Parameters:
dl - Array of the instance references to the objects in dynamic library. See description of this class above for more details.
Returns:
the result fo computation.
Throws:
Throwable - if any runtime error have occured (i.e. division by 0)
See Also:
Evaluator.compile(java.lang.String, gnu.jel.Library, java.lang.Class), Library

evaluate_char

public char evaluate_char(Object[] dl)
                   throws Throwable
Evaluates the expression whose result has type char.

If the type of the result is not a char this function returns always '?', debug version will print a warning to stderr.

Parameters:
dl - Array of the instance references to the objects in dynamic library. See description of this class above for more details.
Returns:
the result fo computation.
Throws:
Throwable - if any runtime error have occured (i.e. division by 0)
See Also:
Evaluator.compile(java.lang.String, gnu.jel.Library, java.lang.Class), Library

evaluate_int

public int evaluate_int(Object[] dl)
                 throws Throwable
Evaluates the expression whose result has type int.

If the type of the result is not a int this function returns always 0, debug version will print a warning to stderr.

Parameters:
dl - Array of the instance references to the objects in dynamic library. See description of this class above for more details.
Returns:
the result fo computation.
Throws:
Throwable - if any runtime error have occured (i.e. division by 0)
See Also:
Evaluator.compile(java.lang.String, gnu.jel.Library, java.lang.Class), Library

evaluate_long

public long evaluate_long(Object[] dl)
                   throws Throwable
Evaluates the expression whose result has type long.

If the type of the result is not a long this function returns always 0, debug version will print a warning to stderr.

Parameters:
dl - Array of the instance references to the objects in dynamic library. See description of this class above for more details.
Returns:
the result fo computation.
Throws:
Throwable - if any runtime error have occured (i.e. division by 0)
See Also:
Evaluator.compile(java.lang.String, gnu.jel.Library, java.lang.Class), Library

evaluate_float

public float evaluate_float(Object[] dl)
                     throws Throwable
Evaluates the expression whose result has type float.

If the type of the result is not a float this function returns always 0.0, debug version will print a warning to stderr.

Parameters:
dl - Array of the instance references to the objects in dynamic library. See description of this class above for more details.
Returns:
the result fo computation.
Throws:
Throwable - if any runtime error have occured (i.e. division by 0)
See Also:
Evaluator.compile(java.lang.String, gnu.jel.Library, java.lang.Class), Library

evaluate_double

public double evaluate_double(Object[] dl)
                       throws Throwable
Evaluates the expression whose result has type double.

If the type of the result is not a double this function returns always 0.0, debug version will print a warning to stderr.

Parameters:
dl - Array of the instance references to the objects in dynamic library. See description of this class above for more details.
Returns:
the result fo computation.
Throws:
Throwable - if any runtime error have occured (i.e. division by 0)
See Also:
Evaluator.compile(java.lang.String, gnu.jel.Library, java.lang.Class), Library

evaluate_void

public void evaluate_void(Object[] dl)
                   throws Throwable
Evaluates the expression whose result has type void.

If the type of the result is not a void debug version will print a warning to stderr.

Parameters:
dl - Array of the instance references to the objects in dynamic library. See description of this class above for more details.
Throws:
Throwable - if any runtime error have occured (i.e. division by 0)
See Also:
Evaluator.compile(java.lang.String, gnu.jel.Library, java.lang.Class), Library

compare

public static int compare(String s1,
                          String s2)


Copyright © 1998-2009 Konstantin L. Metlov All Rights Reserved.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the JEL manual.