假如小弟我有字符串“（5+6）*7+9/3”小弟我要利用这个字符串求得这个式子的得数，在Java里如何用栈实现啊求高手请问

import java.util.*;public class Test {    public static void main(String[] args) throws Throwable {       List<String> list = analyze("(5+6)*7+9/3");       //System.out.println(list);       System.out.printf("%.2f\n", cacl(list));    }    public static List<String> analyze(String exp) throws Exception { //中缀转后缀        if (exp == null) {            throw new Exception ("illegal parameter.");        }        exp = exp.replaceAll("\\s*", "");        final String symbol = "+-*/()"; //运算符        final String[] priority = {"+-", "*/", "()"}; //优先级        Comparator<String> comp = new Comparator<String>() { //运算符优先级比较            public int compare(String s1, String s2) {                int n1=0, n2=0;                for (int i=0; i<priority.length; i++) {                    if (priority[i].indexOf(s1) >= 0) {n1 = i;}                    if (priority[i].indexOf(s2) >= 0) {n2 = i;}                }                return (n1 - n2);            }        };        List<String> list = new ArrayList<String>(); //后缀表达式结果        Stack<String> sym = new Stack<String>(); //运算符栈         StringBuilder buf = new StringBuilder();        for (char c : exp.toCharArray()) {            if (symbol.indexOf(c) >= 0) {                if (buf.length() > 0) {                    String v = buf.toString();                    if (! v.matches("\\d+([.]\\d+)?")) {                        throw new Exception ("illegal varaible("+v+").");                    }                    list.add(v);                    buf.delete(0, buf.length());                }                if (c == '(') {                    sym.push(String.valueOf(c));                } else if (c == ')') {                    String last = "";                    while (sym.size() > 0) {                        last = sym.pop();                        if (last.equals("(")) {                            break;                        } else {                            list.add(last);                        }                    }                    if (!"(".equals(last)) {                        throw new Exception ("illegal express.");                    }                } else if (sym.size() > 0) {                    String s = String.valueOf(c);                    String last = sym.peek();                    if (last.equals("(") || comp.compare(s, last) > 0) {                        sym.push(s);                    } else {                        last = sym.pop();                        list.add(last);                        sym.push(s);                    }                } else {                    sym.push(String.valueOf(c));                }                     } else {                buf.append(c);            }        }        if (buf.length() > 0) {            list.add(buf.toString());        }        while (sym.size() > 0) {            String last = sym.pop();            if ("()".indexOf(last) >= 0) {                throw new Exception ("illigal express.");            }            list.add(last);        }                return list;    }    public static double cacl(List<String> list) throws Exception { //计算        final String symbol = "+-*/()";        Stack<Double> val = new Stack<Double>();        double result = 0;        while (list.size() > 0) {            String s = list.remove(0);            if (symbol.indexOf(s) >= 0) {                double d1 = val.pop();                double d2 = val.pop();                if ("+".equals(s)) {                    result = d2 + d1;                } else if ("-".equals(s)) {                    result = d2 - d1;                } else if ("*".equals(s)) {                    result = d2 * d1;                } else if ("/".equals(s)) {                    result = d2 / d1;                } else {                    throw new Exception ("illegal symbol("+s+").");                }                val.push(result);            } else {                if (!s.matches("\\d+([.]\\d+)?")) {                    throw new Exception ("illegal variable("+s+").");                }                val.push(Double.valueOf(s));            }        }                return result;    }}