https://www.chegg.com/homework-help/following-write-java-statements-perform-requ

Question

https://www.chegg.com/homework-help/following-write-java-statements-perform-requested-operation-chapter-7-problem-6PP-solution-9780132610421-exc

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Explanation / Answer

import java.util.StringTokenizer; import java.util.Stack; public class Calculator { static int precedence(char op) { switch (op) { case '+': case '-': return 5; case '*': case '/': return 10; default: throw new IllegalArgumentException("invalid operator"); } } public static String infixToPostfix(String infix) { StringTokenizer tokenizer = new StringTokenizer(infix); String postfix = ""; Stack opStack = new Stack(); while (tokenizer.hasMoreTokens()) { String token = tokenizer.nextToken(); char c = token.charAt(0); if (Character.isDigit(c)) { postfix += (token + " "); } else { while (!opStack.empty()) { char top = ((Character)opStack.peek()).charValue(); if (precedence(top) >= precedence(c)) { postfix += (top + " "); opStack.pop(); } else { break; } } opStack.push(new Character(c)); } } while (!opStack.empty()) { char top = ((Character)opStack.pop()).charValue(); postfix += (top + " "); } return postfix; } public static int evalPostfix(String postfix) { StringTokenizer tokenizer = new StringTokenizer(postfix); Stack valStack = new Stack(); while (tokenizer.hasMoreTokens()) { String token = tokenizer.nextToken(); char c = token.charAt(0); if (Character.isDigit(c)) { valStack.push(new Integer(token)); } else { int rightVal = ((Integer)valStack.pop()).intValue(); int leftVal = ((Integer)valStack.pop()).intValue(); int rslt; switch (c) { case '+': rslt = leftVal + rightVal; break; case '-': rslt = leftVal - rightVal; break; case '*': rslt = leftVal * rightVal; break; case '/': rslt = leftVal / rightVal; break; default: throw new IllegalArgumentException("invalid postfix expression"); } valStack.push(new Integer(rslt)); } } int rslt = ((Integer)valStack.pop()).intValue(); if (!valStack.empty()) { throw new IllegalArgumentException("invalid postfix expression"); } return rslt; } public static void main(String[] args) { String infix = args[0]; String postfix = infixToPostfix(infix); System.out.println("postfix: " + postfix); int value = evalPostfix(postfix); System.out.println("value: " + value); } }

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