Formula4J

When an expression such as B = m/h^2 is part of your program and never changes, then you can always implement the expression directly in code. For example, you can define a method that takes m and h as parameters, does the math as ordinary hard-coded statements, and then finally returns the value B as a result. That's easy.

But what happens when the expression isn't known when the program is being written? That's not so easy, because now you need a general expression parser. In the simplest cases, or if you have enough time, you might build such a parser yourself. But you may prefer to use a tool that's already built, tested, and ready to use. Formula4j is such a tool.

The Formula4J Java library gives you this:

• it gives you a plain, simple API (JDK 5+) for the run-time evaluation of basic mathematical expressions
• it targets typical business applications, and not scientific applications
• it lets you use functions and variables in your expressions
• it gives you 48 built-in, commonly used functions
• it lets you define new functions in code
• it lets you define new functions in plain text, so end users can extend your program without coding
• it gives you Decimal, a better abstraction than BigDecimal for most business apps
• it helps you avoid common problems related to using floating-point types
• it uses UTF-8, so you can use Greek letters such as α, β, and so on, in your expressions
• it lets you change (or translate) the names of its built-in functions
• it avoids certain kinds of security threats, by avoiding any kind of general eval function, and parsing input according to a grammar limited to mathematical expressions

What formula4j does not give you:

• no string functions (sorry)
• no deep-level control over its internal parser
• no complex numbers, matrices, fancy-pants abstract algebra, and so on