java四则运算-通过逆波兰式求值
import java.util.ArrayList;import java.util.Iterator;import java.util.List;import java.util.Stack;/* *测试 -5*(10/(2*4.5-4)+(-3/1.5+4)*(-2))/(-2/1-(-1))+12=2.0 */public class Calc {// 求四则运算表达式运算结果public static double excute(String value) throws Exception {List<String> list = toList(value);// 按顺序转成数字符号list 即中序表达式list = toSuffixExpressionList(list);// 转成逆波兰式数字符号list 即后序表达式double result = suffix_excute(list);// 求逆波兰式结果System.out.println(value + "=" + result);return result;}// 表达式划分成中序list 即从左到右数字符号分开private static List<String> toList(String value) {// 开始为-时加上0if ("-".equals(value.substring(0, 1))) {value = "0" + value;}int begin = 0;int end = 0;String item;List<String> resultList = new ArrayList<String>();for (int i = 0, len = value.length(); i < len; i++) {item = value.substring(i, i + 1);if (isOperator(item)) {// 负数跳过if ("-".equals(item) && "(".equals(value.substring(i - 1, i))) {continue;}end = i;// 前一个非符号时加上数字if (begin != end) {resultList.add(value.substring(begin, end));}// 加上符号resultList.add(value.substring(end, end + 1));begin = end + 1;}}// 加上最后一个数字if (begin != value.length()) {resultList.add(value.substring(begin));}// System.out.println(value + "=" + list);return resultList;}// 中序list转换成逆波兰式list 左右根private static List<String> toSuffixExpressionList(List<String> list) throws Exception {Stack<String> operatorStack = new Stack<String>();// 符号栈Stack<String> resultStack = new Stack<String>();// 结果栈Iterator<String> iter = list.iterator();while (iter.hasNext()) {String item = iter.next();if (isOperator(item)) {if (")".equals(item)) {// 遇到)时符号栈一直弹出并压入结果栈直到遇到(，弹出(废弃，结束。while (!(operatorStack.isEmpty() || "(".equals(operatorStack.peek()))) {resultStack.push(operatorStack.pop());}// 弹出(if (!operatorStack.isEmpty() && "(".equals(operatorStack.peek())) {operatorStack.pop();} else {throw new Exception("(少了");}} else if ("(".equals(item)) {// 遇到(时直接入符号栈，结束operatorStack.push(item);} else {// 遇到其他运算符时与符号栈顶（若符号栈顶为空或(时直接入符号栈，结束）运算比较 若比栈顶高直接入符号栈，结束// 否则符号栈弹出并压入结果栈 并再执行与符号栈顶比较直到弹入符号栈，结束while (!(operatorStack.isEmpty() || "(".equals(operatorStack.peek()))) {if (compareOperator(item, operatorStack.peek()) < 1) {resultStack.push(operatorStack.pop());} else {break;}}operatorStack.push(item);}} else {// 数字时直接入结果栈resultStack.push(item);}}// 符号栈全部弹出并压入结果栈while (!operatorStack.isEmpty()) {if ("(".equals(operatorStack.peek())) {throw new Exception("(多了");}resultStack.push(operatorStack.pop());}// 结果栈弹出并反序得出最终结果iter = resultStack.iterator();List<String> resultList = new ArrayList<String>();while (iter.hasNext()) {resultList.add(iter.next());}// System.out.println(list + "=" + rtList);return resultList;}// 逆波兰式list 求值// 从左至右扫描表达式，遇到数字时，将数字压入堆栈，遇到运算符时，弹出栈顶的两个数，用运算符对它们做相应的计算（次顶元素 op// 栈顶元素），并将结果入栈；重复上述过程直到表达式最右端，最后运算得出的值即为表达式的结果。private static double suffix_excute(List<String> list) {Stack<Double> resultStack = new Stack<Double>();Iterator<String> iter = list.iterator();Double num1;Double num2;while (iter.hasNext()) {String item = iter.next();if (isOperator(item)) {num2 = resultStack.pop();num1 = resultStack.pop();resultStack.push(doOperator(num1, num2, item));} else {resultStack.push(Double.parseDouble(item));}}return resultStack.pop();}// 比较两运算高低 1 1>2, 0 1=2 -1 1<2private static int compareOperator(String operator1, String operator2) {if ("*".equals(operator1) || "/".equals(operator1)) {return ("-".equals(operator2) || "+".equals(operator2)) ? 1 : 0;} else if ("-".equals(operator1) || "+".equals(operator1)) {return ("*".equals(operator2) || "/".equals(operator2)) ? -1 : 0;}// 这个到不了return 1;}// +-*/基本运算private static double doOperator(Double num1, Double num2, String operator) {if ("+".equals(operator)) {return num1 + num2;} else if ("-".equals(operator)) {return num1 - num2;} else if ("*".equals(operator)) {return num1 * num2;} else if ("/".equals(operator)) {return num1 / num2;}// 这个到不了return -1;}// 是否为运算符private static Boolean isOperator(String value) {return "(".equals(value) || ")".equals(value) || "+".equals(value) || "-".equals(value) || "*".equals(value)|| "/".equals(value);}public static void main(String[] args) {try {excute("-5*(10/(2*4.5-4)+(-3/1.5+4)*(-2))/(-2/1-(-1))+12");} catch (Exception e) {e.printStackTrace();}}}