package com.yeezhao.common.elt;import java.util.Stack;
import java.util.StringTokenizer;/*** 正整数计算器* * @author Administrator -> junhong* @since 2016年12月13日 下午1:22:40*/
public class CaculatorSimulate {private Stack<Character> operator = new Stack<>(); // 操作符private Stack<Integer> operand = new Stack<>(); // 操作数 0-9public void testCaculate() {}public void testOutput() {}/*** 返回计算结果* * @param exp*            正整数的加减乘除表达式* @return*/public Integer caculate(String exp) {if (exp == null || exp.isEmpty()) {System.out.println("invalid exp!");return 0;}StringTokenizer arr = new StringTokenizer(exp, "+-/*()", true);while (arr.hasMoreTokens()) {String text = arr.nextToken().trim();if (text.length() == 0) { // fix '(('continue;}char c = text.charAt(0);if (c == '+' || c == '-') {while (!operator.isEmpty() && ((operator.peek() == '+') || (operator.peek() == '-')|| (operator.peek() == '/') || (operator.peek() == '*'))) {oper(operator, operand);}operator.push(c);} else if (c == '/' || c == '*') {while (!operator.isEmpty() && ((operator.peek() == '/') || (operator.peek() == '*'))) {oper(operator, operand);}operator.push(c);} else if (c == '(') {operator.push(c);} else if (c == ')') {while (operator.peek() != '(') {oper(operator, operand);}operator.pop();} else {operand.push(Integer.parseInt(text));}}while (!operator.isEmpty()) {oper(operator, operand);;}return operand.pop();}public void oper(Stack<Character> operator, Stack<Integer> operand) {Integer num1 = operand.pop();Integer num2 = operand.pop();Character oper = operator.pop();Integer ret = 0;if (oper == '-')ret = num2 - num1;if (oper == '+')ret = num2 + num1;if (oper == '*')ret = num2 * num1;if (oper == '/') {if (num1 == 0) {System.out.println("'0' can not be divided!");} else {ret = num2 / num1;}}operand.push(ret);}public static void main(String[] args) {String[] exps = { "1+2", "3 * (4 + 5)", "(4 + 5) / 3 + (1 + 2*1)" };System.out.println("---***---");for (String exp : exps) {int ans = new CaculatorSimulate().caculate(exp);System.out.println(exp + " ==> " + ans);}}}