这是一个四则混合运算程序,没什么做优化,也没做什么注释,(人啊,总喜欢偷懒的.)

这个版本我已经定为了2.21版本.呵呵.

从最先的1.0到2.0的改动很大.除了运算思想没动处,其它的都在2.0做了重新设计.

这种程序其实网上一大把（算法也好得多）。此仅为无聊找点事情做而已。

/**
*四则混合运算程序
*作者:黄剑武
*时间:2005年4月29日
*版本:2.21
*修改日志:2.0
* 1.更改表达式用户输入方式.
* 2.对用户输入的表达式进行有效性字符过滤.
* 3.使用Double代替原int数值,并且使用严格浮点运算提高运算精度.
* 4.解除对运算数字只能是一位的限制.
* 5.优化了部分代码.
*修改日志:2.1
*   1.加入表达式括号匹配功能.
*修改日志:2.2
*   1.加入表达式处理功能.
*修改日志:2.21
*   1.修改部分语法以支持JDK1.5中的泛型用法.
*/

import java.lang.reflect.Array;
import java.util.*;
import java.util.regex.*;
import java.lang.*;
import java.io.*;

//测试用例:1-3*(4-(2+5*3)+5)-6/(1+2)=23
//测试用例:11.2+3.1*(423-(2+5.7*3.4)+5.6)-6.4/(15.5+24)=1273.4199746835445
class Calculator
{

 public static void main(String[] args) throws IOException
 {
  String str_input;
  double f_output;

  while (true)
  {
   System.out.print("输入表达式: ");
   System.out.flush();
  
   str_input = getString();
   if (str_input.equals(""))
   {
    break;
   }

   Calculator calculator = new Calculator();

   //以下对输入字符串做规则处理
   str_input = calculator.checkExpression(str_input);
   if (str_input.equals(""))
   {
    System.out.println("   表达式出错  ");
   }

   //以下对输入字符串做表达式转换
   Vector<String> v_compute = calculator.getExpression(str_input);

   /*
   for (int i=0;i<v_compute.size();i++ )
   {
    System.out.println("  "+v_compute.get(i));
   }
   */

   //以下进行后缀表达式转换
   Vector<String> v_tmp_prefix = calculator.transformPrefix(v_compute);

   /*
   for (int i=0;i<v_tmp_prefix.size();i++ )
   {
    System.out.println(v_tmp_prefix.get(i));
   }
   */

   //以下进行后缀表达式运算
   f_output = calculator.evaluatePrefix(v_tmp_prefix);

   System.out.println("结果 = " + f_output);

  }
 }

 /**
 *静态方法,用来从控制台读入表达式
 */
 public static String getString() throws IOException
 {
  InputStreamReader isr = new InputStreamReader(System.in);
  BufferedReader br = new BufferedReader(isr);
  String s = br.readLine();
  return s;
 }

 /**
 *输入字符串转换.把从控制台读入的字符串转成表达式存在一个队列中.
 *例:123+321 存为"123""+""321"
 */
 public Vector<String> getExpression(String str)
 {
  Vector<String> v_temp = new Vector<String>();
  char[] temp = new char[str.length()];
  str.getChars(0,str.length(),temp,0);
  String fi = "";
  int x=0,i=0;
  String regex_fig = "[\\.\\d]";                  //匹配数字和小数点
  String regex_operator = "[\\+\\-\\*/\\(\\)]";    //匹配运算符(+,-,*,/)和括号("(",")")
  Pattern p_fig = Pattern.compile(regex_fig);
  Pattern p_operator = Pattern.compile(regex_operator);
  Matcher m = null; 
  boolean b;
  while (i<str.length())
  {
   Character c = new Character(temp[i]);
   String s = c.toString();
   //System.out.println("char c = "+s);
   m = p_operator.matcher(s);
   b = m.matches();

   if (b)
   {
    //System.out.println("matches operator");
    v_temp.add(fi);
    fi="";
    v_temp.add(s);
   }
   m = p_fig.matcher(s);
   b = m.matches();
   if (b)
   {
    //System.out.println("matches fig");
    fi=fi+s;
   }
   i++;
  }
  v_temp.add(fi);

  return v_temp;
 }

 /**
 *转换中序表示式为前序表示式
 */
 public Vector<String> transformPrefix(Vector<String> v_expression)
 {
  Vector<String> v_prefix = new Vector<String>();
  Stack<String> s_tmp = new Stack<String>();
  String regex_float = "+)?";      //匹配正浮点数
  Pattern p_float = Pattern.compile(regex_float);
  Matcher m = null; 
  boolean b;
  String str_elem = "";

  for (int i=0;i<v_expression.size();i++ )
  {
   str_elem = v_expression.get(i).toString();
   m = p_float.matcher(str_elem);
   b = m.matches();
   
   if (b)
   {
    v_prefix.add(str_elem);
   }
   
   if (str_elem.equals("+")||str_elem.equals("-"))
   {
    if (s_tmp.isEmpty())
    {
     s_tmp.push(str_elem);
    }
    else
    {
     while(!s_tmp.isEmpty())
     {
      String str_tmp = s_tmp.peek();

      if ( str_tmp.equals("("))
      {
       break;
      }
      else
      {
       v_prefix.add(s_tmp.pop());
      }
     }
     s_tmp.push(str_elem);
    }
   }
   
   if (str_elem.equals("*")||str_elem.equals("/"))
   {
    if (s_tmp.isEmpty())
    {
     s_tmp.push(str_elem);
    }
    else
    {
     while(!s_tmp.isEmpty())
     {
      String str_tmp = s_tmp.peek();

      if ( str_tmp.equals("(") || str_tmp.equals("+") || str_tmp.equals("-"))
      {
       break;
      }
      else
      {
       v_prefix.add(s_tmp.pop());
      }
     }
     s_tmp.push(str_elem);
    }
   }

   if (str_elem.equals("("))
   {
    s_tmp.push(str_elem);
   }

   if (str_elem.equals(")"))
   {
    while(!s_tmp.isEmpty())
    {
     String str_tmp = s_tmp.peek();
     if (str_tmp.equals("("))
     {
      s_tmp.pop();
      break;
     }
     else
     {
      v_prefix.add(s_tmp.pop());
     }
    }
   }
  }

  while(!s_tmp.isEmpty())
  {
   v_prefix.add(s_tmp.pop());
  }
  return v_prefix;
 }

 /**
 *前缀表示式求值
 */
 public strictfp double evaluatePrefix(Vector<String> v_prefix)
 {
  String str_tmp = "";
  double num1,num2,interAns = 0;
  Stack<Double> s_compute = new Stack<Double>();

  int i = 0;
  while(i<v_prefix.size())
  {
   str_tmp = v_prefix.get(i).toString();
   if (!str_tmp.equals("+") && !str_tmp.equals("-") && !str_tmp.equals("*") && !str_tmp.equals("/"))
   {
    interAns = s_compute.push(Double.parseDouble(str_tmp));
   }
   else
   {
    num2=(Double)(s_compute.pop());
    num1=(Double)(s_compute.pop());
    
    if (str_tmp.equals("+"))
    {
     interAns = num1+num2;
    }
    if (str_tmp.equals("-"))
    {
     interAns = num1-num2;
    }
    if (str_tmp.equals("*"))
    {
     interAns = num1*num2;
    }
    if (str_tmp.equals("/"))
    {
     interAns = num1/num2;
    }
    s_compute.push(interAns);
   }
   i++;
  }
  return interAns;
 }

 /**
 *括号匹配检测
 */
 public boolean checkBracket(String str)
 {
  Stack<Character> s_check = new Stack<Character>();
  boolean b_flag = true;

  for (int i=0;i<str.length();i++)
  {
   char ch = str.charAt(i);
   switch(ch)
   {
    case @#(@#:
     s_check.push(ch);
     break;
    case @#)@#:
     if (!s_check.isEmpty())
     {
      char chx = s_check.pop();
      if (ch==@#)@# && chx!=@#(@#)
      {
       b_flag = false;
      }
     } else {
      b_flag = false;
     }
     break;
    default:
     break;
   }
  }
  if (!s_check.isEmpty())
  {
   b_flag = false;
  }
  return b_flag;
 }

 /**
 *表达式正确性规则处理与校验
 */
 public String checkExpression(String str)
 {
  Stack<Character> s_check = new Stack<Character>();
  Stack<Character> s_tmp = new Stack<Character>();
  String str_result = "";

  String str_regex = "^[\\.\\d\\+\\-\\*/\\(";                  //匹配合法的运算字符"数字,.,+,-,*,/,(,),"
  Pattern p_filtrate = Pattern.compile(str_regex);
  Matcher m = p_filtrate.matcher(str); 
  boolean b_filtrate = m.matches();
  if (!b_filtrate)
  {
   str_result = "";
   return str_result;
  }

  String str_err_float = ".*(,}.*";                      //匹配非法的浮点数.
  Pattern p_err_float = Pattern.compile(str_err_float);
  Matcher m_err_float = p_err_float.matcher(str); 
  boolean b_err_float = m_err_float.matches();
  if (b_err_float)
  {
   str_result = "";
   return str_result;
  }

  for (int i=0;i<str.length();i++)
  {
   char ch = str.charAt(i);
   if (checkFig(ch))
   {
    if (!s_tmp.isEmpty()&&s_tmp.peek()==@#)@#)
    {
     str_result = "";
     return str_result;
    }
    s_tmp.push(ch);
    str_result = str_result+ch;
   }

   switch(ch)
   {
    case @#(@#:
     if (!s_tmp.isEmpty()&&s_tmp.peek()==@#.@#)
     {
      str_result = "";
      return str_result;
     }
     s_check.push(ch);
     if (s_tmp.isEmpty()||(!this.checkFig(s_tmp.peek())&&s_tmp.peek()!=@#)@#))
     {
      str_result = str_result+ch;
     } else {
      str_result = str_result+"*"+ch;
     }
     s_tmp.push(ch);
     break;
    case @#)@#:
     if (!s_check.isEmpty())
     {
      char chx = s_check.pop();
      if (ch==@#)@# && chx!=@#(@#)
      {
       str_result = "";
       return str_result;
      }
     } else {
      str_result = "";
      return str_result;
     }
     if (s_tmp.peek()==@#.@#||(!this.checkFig(s_tmp.peek())&&s_tmp.peek()!=@#)@#))
     {
      str_result = "";
      return str_result;
     }
     s_tmp.push(ch);
     str_result = str_result+ch;
     break;
    case @#+@#:
    case @#-@#:
     if (!s_tmp.isEmpty()&&(s_tmp.peek()==@#+@#||s_tmp.peek()==@#-@#||s_tmp.peek()==@#*@#||s_tmp.peek()==@#/@#||s_tmp.peek()==@#.@#))
     {
      str_result = "";
      return str_result;
     }
     if (s_tmp.isEmpty()||s_tmp.peek()==@#(@#)
     {
      str_result = str_result+"0"+ch;
     } else {
      str_result = str_result+ch;
     }
     s_tmp.push(ch);
     break;
    case @#*@#:
    case @#/@#:
     if (s_tmp.isEmpty()||s_tmp.peek()==@#.@#||(!this.checkFig(s_tmp.peek())&&s_tmp.peek()!=@#)@#))
     {
      str_result = "";
      return str_result;
     }
     s_tmp.push(ch);
     str_result = str_result+ch;
     break;
    case @#.@#:
     if (s_tmp.isEmpty()||!this.checkFig(s_tmp.peek()))
     {
      str_result = str_result+"0"+ch;
     } else {
      str_result = str_result+ch;
     }
     s_tmp.push(ch);
     break;

    default:
     break;
   }
  }
  if (!s_check.isEmpty())
  {
   str_result = "";
   return str_result;
  }

  return str_result;

 }

 private static boolean checkFig(Object ch)
 {
   String s = ch.toString();
   String str_regexfig = "";                  //匹配数字
   Pattern p_fig = Pattern.compile(str_regexfig);
   Matcher m_fig = p_fig.matcher(s) ;
   boolean b_fig = m_fig.matches();
   return b_fig;
 }

};