一个简单的问题

Question

请帮小弟看看这个小程序:
import java.util.*;
public class Caculate
{
/**
 * @param args
 */
double  operator1=0,operator2=0,result=0;
Stack<Character> stack;
public Caculate()
{
stack=new Stack<Character>();
}
public double caculate(String inputString )
{
char ch;
for(int i=0;i<inputString.length();i++)
{
ch=inputString.charAt(i);
if(Character.isDigit(ch))
{
stack.push(ch);
}
else if(ch==' ') break;
else //ch为操作符
{
if(stack.isEmpty())
{
System.out.println("栈空!");
}
else operator1=(double)stack.pop();
if(stack.isEmpty())
{
System.out.println("栈空!");
}
else operator2=(double)stack.pop();
result=getresult(operator1,operator2,ch);
stack.push((char)result);
}
}
 return (double)stack.pop();//这里提示错误:at java.util.Stack.pop(Unknown Source)
}
public double getresult(double x,double y,char ch1)
{
switch (ch1)
{
case '+':
result=x+y;
break;
case '-':
result=y-x;
break;
case '*':
result=x*y;
break;
case '/':
result=y/x;
break;
default:
result=0;
break;
}
return result;
}
public static void main(String[] args)
{
Caculate ca =new Caculate();
Trans tr=new Trans();
double jieguo=0;
try
   {
   String pexpression="3 5 + 6 * 2  4 * -";    
    System.out.println("波兰表达式: "+pexpression);
   jieguo=ca.caculate(poleanexpression);
   System.out.println("(3+5)*6-2*4="+jieguo);
   }
   catch (Exception e) 
   {
 e.printStackTrace();
   }
}}

Answer 1

答：除了以下两句的错误之外：
 Trans tr=new Trans();//错误原因：Trans没有定义
jieguo=ca.caculate(poleanexpression);//错误原因：poleanexpression没有定义
其它都对。
若将：
Trans tr=new Trans();这一句去掉
jieguo=ca.caculate(poleanexpression);改为：
jieguo=ca.caculate(pexpression);运行结果就正常了。

Answer 2

不好意思,我没有把Trans类没有贴出来,应该把Trans tr=new Trans();这一句去掉.但调试时提示return (double)stack.pop();这句出错.我弄了很久,就是没搞定.这个程序要实现的功能很简单,就是根据输入的波兰表达式计算结果.请高手帮帮小弟!
import java.util.*;
public class Caculate
{    
    /**
     * @param args
     */
    double  operator1=0,operator2=0,result=0;
    Stack<Character> stack;
    public Caculate()
    {
        stack=new Stack<Character>();
    }
    public double caculate(String inputString )
    {
        char ch;
        for(int i=0;i<inputString.length();i++)
        {
            ch=inputString.charAt(i);
            if(Character.isDigit(ch))
            {
                stack.push(ch);
            }
            else if(ch==' ') break;
            else //ch为操作符
            {
                if(stack.isEmpty())
                {
                    System.out.println("栈空!");
                }
                else operator1=(double)stack.pop();
                if(stack.isEmpty())
                {
                    System.out.println("栈空!");
                }
                else operator2=(double)stack.pop();
                result=getresult(operator1,operator2,ch);
                stack.push((char)result);
            }
        }        
         return (double)stack.pop();//这里提示错误:at java.util.Stack.pop(Unknown Source)
    }
    public double getresult(double x,double y,char ch1)
    {        
        switch (ch1)
        {
            case '+':
                result=x+y;
                break;
            case '-':
                result=y-x;
                break;
            case '*':
                result=x*y;
                break;
            case '/':
                result=y/x;
                break;
                default:
                    result=0;
                break;
        }
        return result;
    }    
    public static void main(String[] args)
    {
        Caculate ca =new Caculate();
       // Trans tr=new Trans();
        double jieguo=0;
        try
           {
               String pexpression="3 5 + 6 * 2  4 * -";               
                System.out.println("波兰表达式: "+pexpression);
               jieguo=ca.caculate(pexpression);
               System.out.println("(3+5)*6-2*4="+jieguo);
           }
           catch (Exception e) 
           {
             e.printStackTrace();
           }        
    }}

Answer 3

答：楼主5楼贴的代码在JDK1.5下跑，没有任何问题啊。

Answer 4

不会吧,我的JKD可是1.6的了啊,报错啊.