listing stacks and queues continued inputstreamreader isr new inputstreamreader(system in)bufferedreader br new bufferedreader(isr)string br readline()return ///end class postfixapp ///////////////////////////////////////////////////////////////the main(method in the postfixapp class gets the postfix string from the user and then creates parsepost objectinitialized with this string it then calls the doparse(method of parsepost to carry out the evaluation the doparse(method reads through the input string character by character if the character is digitit' pushed onto the stack if it' an operatorit' applied immediately to the two operators on the top of the stack (these operators are guaranteed to be on the stack already because the input string is in postfix notation the result of the arithmetic operation is pushed onto the stack after the last character (which must be an operatoris read and appliedthe stack contains only one itemwhich is the answer to the entire expression here' some interaction with more complex inputthe postfix expression +* +/-which we showed human evaluating in figure this expression corresponds to the infix *( + )- /( + (we saw an equivalent translation using letters instead of numbers in the previous sectiona*( + )- /( +fin infix is abc+*def+/in postfix here' how the postfix is evaluated by the postfix java programenter postfix +* +/ 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) stack (bottom-->top) evaluates to