Expression Resolver

The Expression Resolver for Java provides a very easy way to solve any valid mathematical expression. The string based expression is parsed, and then reduced to a single numeric value. If the experssion was unable to reduce completely, the program tries to give clear error messages, such that the user is notified. (Note: The program escapes all whitespaces and $ signs)

Features

Built-in math operators

• Addition: +
• Subtraction: -
• Multiplication: *
• Division: /
• Exponent: ^
• Parentheses: ( and )

*Note: Numbers/Variables followed directly by ( sign do not get identified as multiplication. Therefore, they must be shown explicitly (Ex. use 2*(1+1) instead of 2(1+1)). However, this is not the case if a - sign is followed by (, -(2*1) is equivalent to -1*(2*1).

Built-in functions

Built-in mathematical constants

• PI (π): pi (3.141592653589793)
• Euler’s number (e): e (2.718281828459045)
• Tau (τ or 2*π): tau (6.283185307179586)

Set up

Apache Maven

<dependencies>
    ...
    <dependency>
        <groupId>com.github.ayaanqui</groupId>
        <artifactId>expression-resolver</artifactId>
        <version>2.0</version>
    </dependency>
</dependencies>

Gradle

allprojects {
    repositories {
        ...
        maven { url "https://jitpack.io" }
    }
}

dependencies {
    ...
    implementation 'com.github.ayaanqui:expression-resolver:master-SNAPSHOT'
}

Usage

To set up ExpressionResolver, first make sure to import all necessary packages.

import com.github.ayaanqui.expressionresolver.Resolver;
import com.github.ayaanqui.expressionresolver.objects.Response;

Once these packages have been imported you can start using Resolver

// Create ExpressionResolver object
Resolver calculator = new Resolver();

A Resolver object gives access to methods:

• setExpression Takes in a string expression
• setFunction Define function
• expressionList
• getExpression Returns expression set using setExpression
• getLastResult Returns last successfully solved expression
• solveExpression Solves the expression set using setExpression or expressionList. Returns Response object

Setting expressions

Resolver res = new Resolver();
// First value
double value1 = res
    .setExpression("473+5711-sin(20)"); // Returns Resolver object
    .solveExpression() // Returns Response object...
    .result; // Holds double value computed by solveExpression()
// Second value
double value2 = res
    .setExpression("sum(53, 577, 19493, 374)"); // Returns Resolver object
    .solveExpression() // Returns Response object...
    .result; // Holds double value computed by solveExpression()

Response object

This object is returned by solveExpression which holds all the information about the solved expression:

• success Returns a boolean value indicating whether the expression was reduced without an error
  • true when the expression was reduced with no error
  • false when there was an error reducing the expression
• result If success == true then result holds the double value of the reduced expression
• errors If success == false then errors holds an String array (String[]) describing each error

Examples

Basic use case

Resolver calculator = new Resolver();
calculator.setExpression("2+2");
double result = calculator.solveExpression().result; // 4
calculator.setExpression("95-10+2^(3+3)*10");
result = calculator.solveExpression().result; // 725.0
calculator.setExpression("sin(20) + pi * 2");
result = calculator.solveExpression().result; // 7.196130557907214

Accessing last result

Using the < operator allows access to the last successfull result

Resolver calculator = new Resolver();
calculator.setExpression("-pi^2");
Response res = calculator.solveExpression();
res.result // 9.869604401089358
calculator.setExpression("2+<");
calculator.solveExpression().result; // 11.869604401089358

Nested parentheses

Detects mismatched, or empty parentheses

Resolver solver = new Resolver();
solver.setExpression("1+((((((((((((1-1))))+2+2))))))))");
double value = solver.solveExpression().result; // 5
solver.setExpression("ln(((((((sin(tau/2))))))))-(((1+1)))");
double v2 = solver.solveExpression().result; // -38.63870901270898
// Mismatch parentheses error:
solver.setExpression("(1-2)/sin((3*2)/2");
Response res = solver.solveExpression();
// Check for errors
if (!res.success)
    System.out.println("Error: " + res.errors[0]); // Error: Parentheses mismatch

Variables

Assigned using the = operator. (Note: once a variable is assigned, the value cannot be changed)

Resolver solver = new Resolver();
// Declaring a new variable
double v1 = solver.setExpression("force = 10*16.46")
                .solveExpression()
                .result; // 164.60000000000002
// Using variable "force"
// force = 164.60000000000002
// pi = pre-defined π constant
double v2 = solver.setExpression("force + pi")
                .solveExpression()
                .result; // 167.7415926535898
// Results in an error (res.success = false)
Response res = solver.setExpression("1 = 2").solveExpression();
if (res.success == false)
    System.out.println("Error:\n" + res.errors[0] + "\n" + res.errors[1]);
// Results in an error (res.success = false)
// All variables are immutable (constant or unchangeable)
Response res = solver.setExpression("pi = 3.142").solveExpression();
if (res.success == false)
    System.out.println("Error:\n" + res.errors[0] + "\n" + res.errors[1]);

Defining functions

Functions can be defined by using setFunction method which takes two parameters: String function name, and Function<Double[], Double> function definition.

Resolver res = new Resolver();
// Defining min function
double minVal = res
    .setExpression("min(45, 9, 22, pi, 644, 004, 192)")
    //           Name   Function Definition
    .setFunction("min", params -> {
        double min = params[0];
        for (double val : params)
            if (val < min)
                min = val;
        return min;
    })
    .solveExpression().result; // pi
// Defining force function
double val = res
    .setFunction("force", params -> {
        return params[0] * params[1];
    })
    .setExpression("force(27, 10)")
    .solveExpression()
    .result;
// Redfining built-in function arcsin
res.setFunction("arcsin", params -> 1 / Math.sin(params[0]));