正则表达式&自定义异常 典型案例

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Test
{

public static void main(String[] args)
{
System.out.println(oper(" 12.3+213.1"));

}

public static float oper(String s)
{
Float res = null;
Pattern p = Pattern
.compile("\\s*(\\d+)(\\.*)(\\d+)\\s*(\\+|-|\\*\\/)\\s*(\\d+)(\\.*)(\\d+)\\s*");
Matcher m = p.matcher(s);

boolean b = m.matches();
if (!b)
{
throw new couldNotCaculateException("匹配错误");
}

String s1 = m.group(1) + m.group(2) + m.group(3);
String s2 = m.group(5) + m.group(6) + m.group(7);

Float f1 = Float.parseFloat(s1);
Float f2 = Float.parseFloat(s2);
if ("+".equals(m.group(4)))
{
res = f1 + f2;
} else if ("-".equals(m.group(4)))
{
res = f1 - f2;
} else if ("*".equals(m.group(4)))
{
res = f1 * f2;
} else if ("/".equals(m.group(4)))
{
if (f2 == 0)
{
throw new couldNotCaculateException("除数不能为o");
}
res = f1 / f2;
}

return res;
}

}

class couldNotCaculateException extends RuntimeException
{

private static final long serialVersionUID = -1127307315212919888L;

public couldNotCaculateException(String msg)
{
super(msg);
}
}