Simple Java library to evaluate math expressions.
Switch branches/tags
Clone or download
Latest commit cb4fcec Jan 5, 2017

java-expr-eval Build Status Release

Simple Java library and command line tool to evaluate math expressions.

Library features

  • Supports +, -, *, /, ^ operators with correct precedence (first ^ is evaluated, followed by * and / and then + and -).
  • Supports logging the parsing/evaluation steps done to a Writer or an OutputStream.
  • Multiple custom exceptions to accurately report syntax errors in expressions.
  • Support for variables, that can be defined in a context (see the javadoc for more information).
  • Support for functions, that can be built-in (like basic trigonometry, logarithms, square root) or user-defined in a context as expression with parameters.
  • Functions support overloading (e.g. you can define two different functions with the same name but different number of arguments in the same context).
  • Functions and variables can be defined as readonly to prevent them to be modified in the context.
  • Support for localization: UI messages emitted by the library (step logging, errors, etc.) can be customized (see below).

CLI tool features

  • Supports reading input from command line arguments, files and stdin, and writing output to stdout or files (see -h or --help for details).
  • Interactive context: variables and functions can be added, changed or removed during the session.

#Documentation Full javadoc is available here. This is always updated from latest commit. See releases page for javadoc of specific versions.

Using the localization helper

Since version 3.1 the strings returned by exceptions toString()s, log entries format, InteractiveExpressionContext UI messages, etc can be customized, for example for localization purposes. To do this, you simply need to call the setMessage(LocalizationHelper.Message, String) method for each message you want to customize, before you call the methods that will emit those messages. The messages are represented by the entries of the LocalizationHelper.Message enumeration. Example:

LocalizationHelper.setMessage(LocalizationHelper.Message.REWRITE_STEP, "The \"%s\" expression can also be written as \"%s\".");
//The following line will print to stdout 'The "3+2" expression can also be written as "(3.0+2.0)".' instead of the default '3+2 can be rewritten as (3.0+2.0)'.
Expression.parse("3+2", new OutputStreamWriter(System.out));

#Using as command line tool To start in interactive mode, just run without arguments (you may need to adjust the JAR filename according to the version):

java -jar javaexpreval-3.0.jar

You will see a prompt where you can type expressions, variable/function assignments and commands (actually context, clear, help and exit); type help at this prompt for more instructions. Other than results, you will notice that all the parsing and evaluation steps will be written to stdout too. Use -q or --quiet on the command line if you want to disable this. Other available command line switches can be used to specify I/O files (-i <file>, -o <file>), if the program must exit at the first error (-f), and if it should exit automatically after evaluating input file and expressions from command line (-b). Use -h or --help for more details. Expressions or commands can be specified as command line arguments too, separated by spaces. Warning: If you write expressions as CLI arguments, quotes may be necessary depending on your shell. For example, on Windows cmd.exe, ^ is a special shell character and won't be passed to the JVM (and to the expression parser), so for example if you write 2^3 the application will read 23. This is easily solved using quotes ("2^3").

#Code example Code:

Writer stdout = new OutputStreamWriter(System.out);
ExpressionContext c = new ExpressionContext();
try {
    //Bind a variable to a value
    c.setVariable("someVar", 5);
    //Define a two-argument version of the log function to calculate a logarithm in the specified base.
    //This won't conflict with the built-in 1-argument log function (which it uses) thanks to overloading.
    c.setFunction("log", Expression.parse("log(x)/log(base)"), "x", "base");
    //Parse and evaluate an expression
    Expression expr = Expression.parse("3.2+log(16, 2)*someVar-6^((15+(-someVar)*2)-3)", stdout); //Log parsing steps to System.out (no 2nd parameter can be specified if no logging is desidered)
    double result = expr.eval(c, stdout); //Evaluate in context c and log evaluation steps to System.out (same here)
    System.out.println("Result = " + result);
}catch(ExpressionException e){


16 can be rewritten as 16.0
 2 can be rewritten as 2.0
-someVar can be rewritten as (-(someVar))
15+(-someVar)*2 can be rewritten as (15.0+((-(someVar))*2.0))
(15+(-someVar)*2)-3 can be rewritten as ((15.0+((-(someVar))*2.0))-3.0)
3.2+log(16, 2)*someVar-6^((15+(-someVar)*2)-3) can be rewritten as ((3.2+(log(16.0,2.0)*someVar))-(6.0^((15.0+((-(someVar))*2.0))-3.0)))
16.0 evaluates to 16.0
log(16.0) evaluates to 2.772588722239781
2.0 evaluates to 2.0
log(2.0) evaluates to 0.6931471805599453
(log(16.0)/log(2.0)) evaluates to 4.0
log(16.0,2.0) evaluates to 4.0
someVar evaluates to 5.0
(log(16.0,2.0)*someVar) evaluates to 20.0
(3.2+(log(16.0,2.0)*someVar)) evaluates to 23.2
someVar evaluates to 5.0
(-(someVar)) evaluates to -5.0
((-(someVar))*2.0) evaluates to -10.0
(15.0+((-(someVar))*2.0)) evaluates to 5.0
((15.0+((-(someVar))*2.0))-3.0) evaluates to 2.0
(6.0^((15.0+((-(someVar))*2.0))-3.0)) evaluates to 36.0
((3.2+(log(16.0,2.0)*someVar))-(6.0^((15.0+((-(someVar))*2.0))-3.0))) evaluates to -12.8
Result = -12.8

#Installing the library to your project This project is built and published with jitpack. If you use maven, add this repository


and this dependency (adjust the version if needed, according to the releases page; a commit hash can be used too)


See the jitpack page for instructions for other build systems (gradle, sbt or leiningen).

#Building from source/contributing This library uses Apache Maven as build system. To build you simply need to mvn package in the project root (where you cloned this repository). This will compile, run tests, and put the JAR and the javadoc in the target/ subdirectory. You can run mvn install if you want to install to your local maven repository.