package com.test;import java.math.BigDecimal;import java.util.Stack;/** * 利用栈实现中缀表达式转后缀表达式,并提供对后缀表达式的计算 * Created by jockiller on 2016/3/4. */public class BiaoDaShi {    public static void main(String[] args) {        String bds = "60/(5-2) + 5 *(20 *(3-1))";        System.out.println(bds);        String hzBds = revertBds(bds);        System.out.println(hzBds);        BigDecimal res = calculate(hzBds);        System.out.println(res);    }    /**     * 对后缀表达式进行计算     * @param hzBds     * @return     */    private static BigDecimal calculate(String hzBds) {        Stack
    
      stack = new Stack<>();        String[] split = hzBds.split(" ");        for (String s : split) {            if (null == s || "".equals(s.trim())) continue;            if (YunSuanFu.isYunSuanFu(s.charAt(0))){                //如果是运算符 则将堆中的两个值拿出来计算 然后放回堆中                stack.push(stackoperate(stack.pop(),stack.pop(),s.charAt(0)));            }else {                stack.push(new BigDecimal(s));            }        }        return stack.pop();    }    /**     * 根据运算符进行计算     * @param v1     * @param v2     * @param c     * @return     */    private static BigDecimal stackoperate(BigDecimal v2, BigDecimal v1, char c) {        YunSuanFu yun = YunSuanFu.parse(c);        switch (yun){            case MULTIPLY:                return v2.multiply(v1);            case DIVIDE:                return v1.divide(v2);            case ADD:                return v1.add(v2);            case MINUS:                return v1.subtract(v2);            default:                throw new RuntimeException("不支持的运算");        }    }    /**     * 中缀表达式转换为后缀表达式     *     * @param bds 中缀表达式     * @return     */    private static String revertBds(String bds) {        Stack
     
       stack = new Stack();        String s = bds.replaceAll(" ", "");        StringBuffer sb = new StringBuffer();        boolean nextPop = false;        char ic;        for (int i = 0; i < s.length(); i++) {            if (YunSuanFu.isYunSuanFu(ic = s.charAt(i))) {                if (nextPop) {                    nextPop = false;                    sb.append(" ").append(stack.pop());                    sb.append(" ").append(stack.pop());                }                //判断当前运算符是否是右括号                if (ic == YunSuanFu.RIGHT.ele) {                    //将栈中上一个左括号之前的运算符出栈                    while (true) {                        if ((ic = stack.pop()) != YunSuanFu.LEFT.ele) {                            sb.append(" ").append(ic);                        } else {                            // 如果左括号之前的一个运算符是或者除 那么也需要出栈                            if (stack.peek() == YunSuanFu.DIVIDE.ele || stack.peek() == YunSuanFu.MINUS.ele) {                                sb.append(" ").append(stack.pop());                            }                            break;                        }                    }                } else if (stack.size() > 1 && YunSuanFu.isPriorityHigh(ic, stack.peek())) {                    //判断当前栈中是否有一个运算符 并且新运算符的优先级高于当前优先级,如果是 则下一位的数字输出 并将栈中的两个运算符出栈                    nextPop = true;                    stack.push(ic);                    sb.append(" ");                } else {                    //如果是运算符 则入栈                    stack.push(ic);                    sb.append(" ");                }            } else {                sb.append(ic);            }            if (i == s.length() - 1) {                int size = stack.size();                for (int j = 0; j < size; j++) {                    sb.append(" ").append(stack.pop());                }            }        }        return sb.toString();    }    private enum YunSuanFu {        ADD('+'),        MINUS('-'),        MULTIPLY('*'),        DIVIDE('/'),        LEFT('('),        RIGHT(')'),;        private char ele;        YunSuanFu(char ele) {            this.ele = ele;        }        /**         * 判断是不是运算符         *         * @param c         * @return         */        public static boolean isYunSuanFu(char c) {            for (YunSuanFu fu : YunSuanFu.values()) {                if (fu.ele == c) {                    return true;                }            }            return false;        }        /**         * 转换运算符         *         * @param c         * @return         */        public static YunSuanFu parse(char c) {            for (YunSuanFu fu : YunSuanFu.values()) {                if (fu.ele == c) {                    return fu;                }            }            throw new RuntimeException("未知运算符");        }        /**         * 判断第一个运算符优先级是否高于第二个         *         * @param c1         * @param c2         * @return         */        public static boolean isPriorityHigh(char c1, char c2) {            if ((c1 == MULTIPLY.ele || c1 == DIVIDE.ele) && (c2 == ADD.ele || c2 == MINUS.ele)) {                return true;            }            return false;        }    }}