How to evaluate a math expression given in string form?

javascript

prompt-engineering

math-expression-evaluation

parser-libraries

byAlex Kataev·Feb 17, 2025

With Java's built-in ScriptEngineManager, you can easily evaluate a mathematical expression presented as a string. This condensed snippet succinctly demonstrates the process:

import javax.script.ScriptEngineManager;
import javax.script.ScriptEngine;

public class QuickMathEval {
    public static void main(String[] args) throws Exception {
        ScriptEngine engine = new ScriptEngineManager().getEngineByName("JavaScript");
        System.out.println("Numbers value life too: " + engine.eval("3 + 2 * (4 - 1)")); // Outputs "Result: 9"
    }
}

To go about this, initiate a ScriptEngine from ScriptEngineManager, then call eval with your mathematical string. This single call simultaneously deconstructs and computes the provided expression.

In-depth dive into nested expressions

In terms of managing parentheses and nested expressions, the ScriptEngine performs admirably. But for a heavier, more customisable workload, you may want to look into recursive descent parsers.

Such parsers handle the nuances of operator precedence and associativity with efficiency. Libraries like mXparser are exceptional as they can process more intricate equations and even user-defined functions. Engaging with a customised library can be a major time saver and guarantees that advanced mathematical prerequisites are met.

Razor-sharp focus on efficiency and precision

The JavaScript engine, while excellent for quick evaluations, may falter where accuracy and efficiency are paramount, such as scientific computations. Here, it's prudent to consider libraries offering high-precision data types such as BigDecimal or those facilitating compiled expressions, allowing you to evaluate them with different values, optimising performance for repeat calculations.

Play nice with boolean operations

When dealing with boolean logic, your evaluator choice becomes even more vital. Libraries like EvalEx come into their own here, seamlessly handling boolean operators along with mathematical operations, solidifying their value in these contexts.

Unlock possibilities with custom functions

Should your operational needs include custom functions or variables, focus on libraries that offer these features. These give rise to an evaluator that can morph to fit your application's unique needs.

Craft your own evaluator

While creating your own evaluator may seem like a monumental task, it could turn out to be a highly beneficial learning experience. Familiarising yourself with lexical analysis is key, and with lexer and parser generators such as ANTLR, building such an evaluator becomes feasible. You will also find tons of open-source resources, the best stepping stones towards developing your custom math expression parser.

Insight into advanced use cases

Developing mobile applications? Tools like the Scalar Calculator illustrate the meshing of advanced parsing techniques. Concrete examples like these can be a source of inspiration and provide practical insights into parsing's complex art.

Merging into real-world applications

Implementing these techniques into Java applications becomes an easier task with the aid of open-source libraries. In addition to enabling access to comprehensive documentation for faster integration, these pre-built libraries can handle a range of expression formats and use cases.

When searching for libraries to integrate, focus on examples that align with your application's requirements, whether it's elementary arithmetic or advanced mathematical operations. Choose a library that aligns with your project's requirements and holds a proven record of reliability.

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