初学java，求助。 - Java / Java SE

写了个简单的中缀表达式求值，一直调不过，麻烦各位大侠帮忙指正，代码如下

目标输入：（1+2）* 3 + （5/1）
目标输出： 14

package simplecomputer;

import java.util.Scanner;
import java.util.Stack;

public class Caculator
{
public String compute(String expression)
{
String exp = expression.trim();
char[] strs = exp.toCharArray();

Stack<String> operatorStack = new Stack<String>();
Stack<String> valueStack = new Stack<String>();

String topOperator = "";
String operandOne = "";
String operandTwo = "";

Double result = new Double(0.0);

for (int i = 0; i < strs.length; i++)
{
String pointer = String.valueOf(strs[i]);
Character next = new Character(pointer.charAt(0));

switch (next)
{
case '+':case '-':case '*':case '/':
if(operatorStack.isEmpty())
{
operatorStack.push(pointer);
}
else
{
topOperator = operatorStack.peek();
Character a = topOperator.charAt(0);
while (priority(next) <= priority(a))
{
topOperator = operatorStack.pop();
operandTwo = valueStack.pop();
operandOne = valueStack.pop();
Double num1 = Double.parseDouble(opera