public class StackDriver $\{$ public static void main$($String $[]$args$)\{$ Scanner in $=$ new Scanner$($System$.$in$)$; System.out.print$("$Enter any parenthesized expression: $")$; String s $=$ in$.$nextLine$()$; while $(!$quit$)\{$ System.out.println$("$Menu:$")$; System.out.println$("1.$ Enter a fully parenthesized expression."$)$; System.out.println$("2.$ Evaluate a fully parenthesized expression."$)$; System.out.println$("3.$ Convert a fully parenthesized expression to post$-$fix."$)$; System.out.println$("4.$ Evaluate post$-$fix."$)$; System.out.println$("5.$ Quit"$)$; System.out.print$("$Enter your choice: $")$; int choice $=$ in$.$nextInt$()$; in$.$nextLine$()$; switch $($choice$)\{$ case $1$: System.out.print$("$Enter a fully parenthesized expression: $")$; expression $=$ in$.$nextLine$()$; if $($isLegal$($expression$))\{$ System.out.println$($expression $+"$ is a legal expression."$)$; $\}$ else $\{$ System.out.println$($expression $+"$ is not a legal expression."$)$; $\}$ break; case $2$: if$(!$expression.isEmpty$())\{$ evaluateExpr$($expression$)$; $\}$ else $\{$ System.out.println$("$No expression entered."$)$; $\}$ break; case $3$: if $(!$expression.isEmpty$())\{$ String postFix $=$ convertToPostfix$($expression$)$; System.out.println$("$Post$-$fix notation: $"+$ postFix$)$; $\}$ else $\{$ System.out.println$("$No expression entered."$)$; $\}$ break; case $4$: System.out.println$("$Would you like to enter a new post$-$fix expression? $($y$/$n$)")$; String useExisting $=$ in$.$nextLine$()$; if $($useExisting$.$equalsIgnoreCase$("$y$"))\{$ System.out.print$("$Enter post$-$fix expression: $")$; String postFix $=$ in$.$nextLine$()$; evaluatePostfix$($postFix$)$; $\}$ else if $(!$expression.isEmpty$())\{$ String postFix $=$ convertToPostfix$($expression$)$; evaluatePostfix$($postFix$)$; $\}$ else $\{$ System.out.println$("$No expression available."$)$; $\}$ break; case $5$: quit $=$ true; System.out.println$("$Exiting program..."$)$; break; default: System.out.println$("$Invalid choice."$)$; $\}\}$ public static String convertToPostfix$($String str$)\{$ StringBuilder result $=$ new StringBuilder$()$; ListStack operators $=$ new ListStack$()$; for $($int i $=0$; i $<$ str$.$length$()$; i$++)\{$ char ch $=$ str$.$charAt$($i$)$; if $($Character$.$isDigit$($ch$))\{$ result.append$($ch$).$append$(\text{'}\text{'})$; $\}$ else if $($ch $==\text{'}(\text{'})\{$ operators.push$($ch$)$; $\}$ else if $($ch $==\text{'})\text{'})\{$ while $(($char$)$ operators.top$()!=\text{'}(\text{'})\{$ result.append$(($char$)$ operators.topAndPop$()).$append$(\text{'}\text{'})$; $\}$ operators.pop$()$; $\}$ else if $($ch $==\text{'}+\text{'}||$ ch $==\text{'}-\text{'}||$ ch $==\text{'}*\text{'}||$ ch $==\text{'}/\text{'}||$ ch $==\text{'}\%\text{'})\{$ while $(!$operators.isEmpty$())\{$ result.append$(($char$)$ operators.topAndPop$()).$append$(\text{'}\text{'})$; $\}$ operators.push$($ch$)$; $\}\}$ while $(!$operators.isEmpty$())\{$ result.append$(($char$)$ operators.topAndPop$()).$append$(\text{'}\text{'})$; $\}$ return result.toString$().$trim$()$; $\}$ public static void evaluatePostfix$($String postfix$)\{$ ListStack stack $=$ new ListStack$()$; for $($int i $=0$; i $<$ postfix.length$()$; i$++)\{$ char ch $=$ postfix.charAt$($i$)$; if $($Character$.$isDigit$($ch$))\{$ stack.push$(($int$)($ch $-\text{'}0\text{'}))$; $\}$ else if $($ch $==\text{'}+\text{'}||$ ch $==\text{'}-\text{'}||$ ch $==\text{'}*\text{'}||$ ch $==\text{'}/\text{'}||$ ch $==\text{'}\%\text{'})\{$ int op$2=$ stack.topAndPop$()$; int op$1=$ stack.topAndPop$()$; switch $($ch$)\{$ case $\text{'}+\text{'}$: stack.push$($op$1+$ op$2)$; break; case $\text{'}-\text{'}$: stack.push$($op$1-$ op$2)$; break; case $\text{'}*\text{'}$: stack.push$($op$1*$ op$2)$; break; case $\text{'}/\text{'}$: stack.push$($op$1/$ op$2)$; break; case $\text{'}\%\text{'}$: stack.push$($op$1\%$ op$2)$; break; $\}$System$.$out.println$("$Postfix result: $"+$ stack.topAndPop$())$;