Java Expression Parser & Calculator Shunting Yard Algorithm

Question

So the task is to create our own parser for a expression calculator. For Example:

Input: 3+2*1-6/3 Output: 3

Input: 3++2 Output: Invalid Expression

Input

Answer 1

Couldn't you use the javascript scripting engine? (you would need a bit of tweaking for the 5--2 expression) The code below outputs:

3+2*1-6/3 = 3.0
3++2 = Invalid Expression
-5+2 = -3.0
5--2 = 7.0

Code:

public class Test1 {

    static ScriptEngine engine;

    public static void main(String[] args) throws Exception {
        engine = new ScriptEngineManager().getEngineByName("JavaScript");

        printValue("3+2*1-6/3");
        printValue("3++2");
        printValue("-5+2");
        printValue("5--2");
    }

    private static void printValue(String expression) {
        String adjustedExpression = expression.replaceAll("--", "- -");
        try {
            System.out.println(expression + " = " + engine.eval(adjustedExpression));
        } catch (ScriptException e) {
            System.out.println(expression + " = Invalid Expression");
        }
    }
}