String-Calculator

Java class to evaluate Mathematical Strings

Abstract

String-Calculator is a Java-Class to safely evaluate a Mathematical Equation. This Equation can be (e.g.) from a User.

From Basic Operators like plus and minus it features also small helpful additions like the °-suffix to convert degrees to radian (90° => π/4) to be able to execute sin() or cos() in an easy manner (sin(90°)) instead with the complicated usage of rad() (sin(rad(90))).

It is designed to make it easy to customize the Calculator by adding custom functions, variables or even operators. It is also possible to overwrite an existing operator (eg calculator.setExpressionOperator('+', (a, b) -> 2*a + 2*b);, 2+2 => 8) or to create a completely new operators (eg calculator.setPrefixOperators('~', (x) -> Math.round(x));, ~0.6845 => 1.0)

Usage Example

import hwr.oop.stringcalculator.StringCalculator;

class CalculatorProgram{
    public static void main(String[] args){
        StringCalculator calculator = new StringCalculator();
        calculator.setVariable("x", 5);
        
        double result = calculator.solve("2*x²-4");  // 46
        
        System.out.print("Result: ");
        System.out.println(result);
    }
}

Feature List

Meaning	Icon
Successful:	️✅
Failed:	❌️
Not Tested/Implemented:	️❔

Feature	Tests
Basic Operations (+,-,*,/)	️✅️
Custom Basic Operations	️✅️
Prefix Operators (+,-,~)	️✅️
Custom Prefix Operators	️✅️
Suffix Operators (!,°,²,³)	️✅️
Custom Suffix Operators	️✅️
Functions (sin, sqrt, log)	️✅️
Custom Functions	️✅️
Constants (π,ⅇ)	️✅️
Custom Variables	️✅️

Additional Dependencies

No Additional Dependencies Required

Number	Dependency Name	Dependency Description	Why is it necessary?
1	/	/	/

Problems during development

• order of operations (e.g. Multiplication before Addition)
• Rounding Errors during tests (e.g. result is 0.99999999 instead of 1.0)
• how to save functions/callable

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Complete Index of all (default) Operations

Order of Operations priority

Priority	Name
6	Numbers/Variable/Functions
5	Suffix-Operators
4	Factor-Operators
3	Prefix-Operator
2	Term-Operators
1	Expression-Operators

Expression Operators

Name	Operator	Example
Addition	+	2+3 => 5
Subtraction	-	5-4 => 1

Term Operators

Name	Operator	Example
Multiplication	*	2*3 => 6
Division	/	9/3 => 3
Modulo/Remainder	\	8\3 => 2

Factor Operators

Name	Operator	Example
Pow	^	2^3 => 8

Prefix Operators

Name	Operator	Example
Positive	+	+5 => 5
Negative	-	-5 => -5
Round	~	~3.1415 => 3

Suffix Operators

Name	Operator	Example
Faculty	!	4! => 24
Degrees	°	180° => pi
Percent	%	34% => 0.34
Square	²	3² => 9
Cubic	³	3³ => 27

Constants Operators

Functions	Name	Example
π	pi	pi => 3.1415...
ⅇ	e	e => 2.7182...

Functions Operators

Functions	Name	Example
Sine	sin()	sin(pi/2) => 1.0
Arc Sine	asin()	asin(1) => pi/2
Cosine	cos()	cos(0) => 1.0
Arc Cosine	acos()	acos(1.0) => 0
Tangent	tan()	tan(pi/4) => 1.0
Arc Tangent	atan()	atan(1.0) => pi/4
To Radians	rad()	rad(180) => pi
To Degrees	deg()	deg(pi) => 180
Absolute	abs()	abs(-8) => 8
Square Root	sqrt()	sqrt(9) => 3
Log (Basis ⅇ)	log()	log(e³) => 3
Log (Basis 10)	log10()	log(10³) => 3