Dynamic expression evaluater

Question

I have a dynamic expression of this sort:
{ (( A || B ) && ( C || D )) || E }
where A,B,C,D,E...(and so on) are boolean variables and the operators between them keep changing.
How can i do this through some methods?

Answer 1

If the expression is valid java syntax, then consider writing a piece of code that writes a piece of java with a method containing your expression, and where the letters in the expressions are local variables.
Then invoke the compiler on the generated code using Runtime.exec, load the class and use it.
How fast is this process you might ask? The slowest I have seen was one and a half second on a 550 MHz PIII W2K PC, the fastest was down around 0.01 second, on a recent Athlon with SCSI disks and Linux.
Of course as soon as the class is loaded it is a method call like any other one, so if you want to invoke the expression many times with different values the runtime cost is only the cost of as many method calls, you don't have to regenerate the java again until you change the expression.
You can trade simplicity of implementation for load time speed by generating the class file directly without using java source code as an interim format. O'Reilly has a book on how to write "assembler" for the JVM that explains how to do this. You won't be touching the disk system at all, but will be writing the bytes of a class definition directly to the ClassLoader.defineClass method