stack (bottom-->top) stack (bottom-->top) stack (bottom-->top) stack (bottom-->top) stack (bottom-->top) stack (bottom-->top) stack (bottom-->top) stack (bottom-->top) stack (bottom-->top) stack (bottom-->top) evaluates to as with the last programpostfix java doesn' check for input errors if you type in postfix expression that doesn' make senseresults are unpredictable experiment with the program trying different postfix expressions and seeing how they're evaluated will give you an understanding of the process faster than reading about it summary stacksqueuesand priority queues are data structures usually used to simplify certain programming operations in these data structuresonly one data item can be accessed stack allows access to the last item inserted the important stack operations are pushing (insertingan item onto the top of the stack and popping (removingthe item that' on the top queue allows access to the first item that was inserted the important queue operations are inserting an item at the rear of the queue and removing the item from the front of the queue queue can be implemented as circular queuewhich is based on an array in which the indices wrap around from the end of the array to the beginning priority queue allows access to the smallest (or sometimes the largestitem the important priority queue operations are inserting an item in sorted order and removing the item with the smallest key these data structures can be implemented with arrays or with other mechanisms such as linked lists ordinary arithmetic expressions are written in infix notationso-called because the operator is written between the two operands in postfix notationthe operator follows the two operands arithmetic expressions are typically evaluated by translating them to postfix notation and then evaluating the postfix expression