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

Here you are:

private static final ScriptEngine engine = new ScriptEngineManager().getEngineByName("JavaScript");

public static String eval(String matlab_expression){
    if(matlab_expression == null){
        return "NULL";
    }
    String js_parsable_expression = matlab_expression
            .replaceAll("\\((\\-?\\d+)\\)\\^(\\-?\\d+)", "(Math.pow($1,$2))")
            .replaceAll("(\\d+)\\^(\\-?\\d+)", "Math.pow($1,$2)");
    try{
        return engine.eval(js_parsable_expression).toString();
    }catch(javax.script.ScriptException e1){
        return null; // Invalid Expression
    }
}