问题
I'm looking to figure out the answer to this problem here.
First off,
blah[abc] = blah[abc].replaceAll("(.*) (.*)", "$2, $1");
Can someone explain to me what the (.*), $2 and $1 are?
Secondly, when I nest that within a for statement in order to reverse two parts of a string, I am hit with an exception error. I was wondering if anybody knew why that is.
Thanks
Edit: This is the error I receive
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 1 at ChangeNames.main(ChangeNames.java:21)
回答1:
(.*) - would be a pattern to match any number of characters. Parentheses would be to mark it as a sub pattern (for back reference).
$2 & $1 - are back references. These would be things matched in your second and first sub pattern.
Basically replaceAll("(.) (.)", "$2, $1") would find characters separated by a space, then add a comma before the space, in addition to flipping the parts. For example:
a b => b, a
Hello world => Hellw, oorld
Not sure about nesting... Can you post the code you're running?
回答2:
Your regular expression "(.)(.)" will be of this sort : "(x)(y)" this will be replaced by "$2,$1.
来源:https://stackoverflow.com/questions/5189415/java-understanding-the-string-replaceall-method