Computer Science 1 : Java Programming Dr. David Cline Program: Postfix Calculator In this program, you will write a command line calculator that can evaluate simple mathematical expressions on typed in postfix notation (also called reverse polish notation, or RPN), as well as store varlables for later use in other expressions. Postfix notation: In a typical mathematical expression that you are probably used to, such as 52, the operator() goes in-between the two operands (5 and 2). This is called "infix" notation. Postfix notation places the two operands first, and the sign last, giving 52+. One of the main benefits of postfix notation is that it is easy to evaluate usinga stack. Parentheses are not needed, nor are precedence rules, since there is only one reasonable way to evaluate the expression. The algorithm to do this uses a stack of numbers, and can be stated in a few steps as follows: break it into tokens, and initialize an empty stack of Given a Postfix expression suchas 23+x numbers. Then do the following steps: L Process the tokens from left to right. For each token, If the token is an operand (a number or variable), push the value of the operand on the stack (of doubles in our case). For an operator or function(+sin), pop the needed number of operands off the stack, compute the result, and push it back on the stack 2 The expression's value will be on the top of the stack at the end. Error checking is also easy. The following are error conditions L If at any point there are not enough operands for an operation on the stack, the postfix expression is not valid. 2 If more than one value is on the stack at the end, the expression is not valid. Memory: Your calculator must have a memory that allows it to store or modify named variables. These can easily be stored in a HashMap, or parallel ArrayLists