Postfix Evaluation 2

Write a class, PostfixEvaluator, that evaluates a postfix expression. The class should contains a main method that accepts the expression as a command line argument and outputs the value of the expression or an appropriate error message if the expression is not in proper form.

• The operands are of type double
• The legal operators are +, -, *, /, and ^ (power)
• The expression should be parsed using Scanner (constructed from the argument string), and thus all elements of the expression -- operands delimiters -- may be assumed to be whitespace-separated
• Assume the exception class ParenCheckerException is available, and has a constructor that accepts a String (the message of the exception)

Here is a typical set of executions of the class:

$ java PostfixEvaluator "1.5"
1.5
$ java PostfixEvaluator "1.5 2 +"
163.0
$ java PostfixEvaluator "1.5 + 2"
*** ERROR *** Missing left operand
$ java PostfixEvaluator "2 3"
*** ERROR *** Extra operands in expression
$ java PostfixEvaluator "2 +"
*** ERROR *** Missing left operand
$ java PostfoxEvaluator "+"
*** ERROR *** Missing both operands
$ java PostfixEvaluator ""
*** ERROR *** Empty expression