Presents your  
JAVA E-NEWSLETTER for January 22, 2004 
 
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PARSE JAVA MATHEMATICAL EXPRESSIONS WITH JEP   
  
JEP is a Java mathematical expression parser. This means that you can 
pass JEP a string of mathematical operations (which may also contain 
variables) to perform and get back an answer.   
  
To start using JEP, create an instance of the parser:   
  
JEP j = new JEP();   
  
Then, if you plan on using functions such as sin or cos, you need to 
tell JEP to expect these by calling the parser's addStandardFunctions 
method:   
  
j.addStandardFunctions();   
  
You're ready to start parsing. Call the parseExpression method with the 
expression that needs parsing. In this case, we'll parse whatever is 
passed from the command line:   
  
j.parseExpression(args[0]);   
  
Now print the result:   
  
System.out.println(j.getValue());   
  
For example, if the expression was "75 * 4 / (3 * 100)", the output 
would be:   
  
1.0   
  
If you want to use variables in your expression, you must tell JEP to 
expect these variables by calling the parser's addVariable method:   
  
j.addVariable("x", 0);   
  
One thing to keep in mind if you decide to use JEP in your code is that 
JEP comes with one of two licenses: GPL or commercial. Depending on the 
environment you plan on using it in, the license type may be important
to 
you.   
  
Below is a complete example that parses the expression passed in as a 
command line argument.   
  
import org.nfunk.jep.JEP;   
  
public class JepTip {   
    public static void main(String []args) {   
        JEP j = new JEP();   
  
        j.addStandardFunctions();   
  
        j.parseExpression(args[0]);   
  
        System.out.println(j.getValue());   
    }   
}   
  
Visit the JEP Web site to get complete documentation and plenty of 
sample code.   
http://www.singularsys.com/jep/   
  
David Petersheim is the Director of Application Development with 
Genscape, Inc. He designs and develops server-side applications to
acquire and 
process real-time energy data.   
  
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