近来用JAVA写了一个小程序,不敢独享.

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 = "\\d+(\\.\\d+)?"; //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 = ".*(\\.\\d*){2,}.*"; //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 = "\\d"; //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;
}

};