异常：Dangling meta character '?' near index 0

Problem 

转载自：http://www.javagalaxy.com/forum/viewtopic.php?p=377&sid=2d2152ff1ee06bc37c31b4b40e9a6fad

String str = "testing??"; 

str = str.replaceAll("?", ""); 

When you use the above pattern you get an exception as "Dangling meta character '?' near index 0" 


Solution 

String str = "testing??"; 

str = str.replaceAll("\\?", ""); 

You can use the above solution when you are replacing * and + symbols 

String str = "testing??*+"; 

str = str.replaceAll("\\*", ""); //"Dangling meta character '*' near index 0" 
str = str.replaceAll("\\+", ""); //"Dangling meta character '+' near index 0"

 

+、*、|、/等符号在正则表达示中有相应的不同意义。
一般来讲只需要加[]、或是//即可

int i=s.split("[?]").length;

或者

int i=s.split("\\?").length;i);