String.replaceAll (".", "\ \") The error problem

  	public static void main(String[] args) {
  		String s = "a";
  		s = s.replaceAll(".", "\\");
  	}
  

above procedure given as follows:
java.lang.StringIndexOutOfBoundsException: String index out of range: 1

what is the reason ? Thank you !
------ Solution ---------------------------------------- ----
replaceAll parameter is the regex, regular expressions , the first will escape , so the error .
the program can be changed to the following

  public static void main(String[] args) {
  	    String s = "a";
  	    s = s.replaceAll(".", "\\\\");
  	}
  

------ Solution ------------------------------------- -------
java replaceAll () method to use four backslash represents a backslash

example str1 = "aa \ bbb"; str2 = "aa'bbb";

To replace str1 = "aa \ \ bbb"; str2 = "aa \ 'bbb";

must replace this :

str1 = str1.replaceAll ("\ \ \ \", " \ \ \ \ \ \ \ \ " ) ;
str2 = str2.replaceAll ("'", "\ \ \ \ ' " ) ;

for the following reasons :

String of replaceAll () method is actually using regular expressions to match the rule ,

\ \ \ \, java resolves to \ \ to regular expressions , regular expressions, and then after a conversion , the \ \ converted into \

which is to use regular java to represent a \ must be written 4 \

If you said \ \ , then write 8 \


So if written : str1 = str1.replaceAll ("\ \", "\ \ \ \");

error will be reported regular expressions .
------ Solution ---------------------------------------- ----

It seems that the amount of my explanation is not in place , +1
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shortly before seen, specific links in this http://bbs.csdn.net/topics/200023433
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regex in \ \ represents \
The java language \ \ represents the character \ , and therefore represents two \ \ must use \ \ \ \