Chapter: Evaluating postfix expressions

Read section 6.2 on using stacks to evaluate postfix expressions. Grab the authors' code from chapter 6 for Postfix.java and PostfixEvaluator.java. You will need to make a small number of changes:

• Remove the line import jss2.LinkedStack
• Change every occurrence of LinkedStack to just Stack
• Surround each push and pop with a try clause and catch the appropriate exception. There is no need to do anything special when you catch the exception so your code may well look like:

          try {
              op2 = (stack.pop()).intValue();
              op1 = (stack.pop()).intValue();
          }
          catch (EmptyStackException ese) {}
  

• Since some variables are now only given values within "try" clauses you will need to make sure that they receive some kind of default value.

Exercise 2