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正则表达式&自定义异常 典型案例，
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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);
}
}
