3. Using Stacks(java.util.Stack), write a program that evaluates a prefix arithmetic expression with single-digit integer operands and operators '-', '+', '*", and 'l". For simplicity, assume that your input string representing the expression does not have any errors (e.g., is valid - no error detection is needed), and that it contains only digits and operator characters (e.g., no spaces). 6 int Yau might nto use the sring ibrary method charAlint m) public static int prefixExpr (String expr)