//to check if numeric
    public boolean checkNumeric(String user_input)
    {
        for( ; x <= user_input.length() ; x++ )
        {
            if(!Char.isDigit(user_input.charAt(x)))
            {
                return flag;
            }
        }
    
        return noError;
    }

it says: cannot find symbol variable- char
Help please.

There is no class called "Char". And you gave us the wrong error message, I'm pretty sure your compiler said "cannot find symbol - Char"