Parse mathematical expressions with JEP

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Parse 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 licences: GPL or commercial. Depending on the environment you plan on using it in, the licence type may be important to you.

Below is a complete example that parses the expression passed in as a command line argument.

Code Select Expand

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()); } }

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