Replacing a String

[Nischal Tanna]

Hi guys..
I have an interesting doubt!!!

I have a String
str = "here's a java's guys"
Suppose i want the above String as below
"here\'s a java\'s guys"
i.e., i want to replace ' with \'...I dont want to use StringTokenizer or StringBuffer..is it possible any other interesting way?..

[Richard Scothern]

String.replaceAll(String, String) ?
Richard

[Wayne L Johnson]

The only "tricky" thing about this case is using a back-slash (\) which has special meanings in regular expressions. Here's what you'll need:

String before = "here's a java's guys";
String after  = before.replaceAll("'", "\\\\'");
System.out.println("AFTER: " + after);

Yes, you need all four back-slashes ...

[anitha selvaraj]

hi,
will u plz. tell me reason, why it requires all the 4 slashes?
what i thought is, only "\'" is enough to replace "'".
thanks in advance

[fred rosenberger]

the backslash has special meaning when quoted in a string. it says "treat the next character as something other that what you normally do with it".
so, you want a backslash and a single quote. if you just did "\'", java reads this as "hey, i have a backslash. i better do something special with the next character.... AH.. it's a single quote. i'll do something with it".
I don't know exactly what it would do, but it definatly wouldn't give you what you want.
so, you need at least "\\". java reads this as "hey, i have a backslash. i better do something special with the next character.... AH.. it's a backslash. what i do special with a backslash is print it (as oppposed to using it to flag the next char. as special)"
in other words, to print a single backslash in a string, you need to type in 2.
why you would need all four, i don't know (but in my defense, i've had no coffee yet this morning).
hope that helps a little.

[Wayne L Johnson]

Fred is on the right track. A single back-slash is used as an escape character, indicating to Java that the next character has special meaning. Thus "t" means the character lower-case 't', while "\t" means a tab. To get a *real* backs-slash you have to use "\\".
The String.replaceAll() method uses regular expressions behind the scenes. And guess what? the back-slash has special meaning when used in regular expressions. So you have to escape the back-slash a second time.
So you type in four back-slashes: "\\\\" and Java interprets that internally as a String with two back-slashes. That new string is then passed to the "replaceAll(...)" method and the regular expression engine interprets the two back-slashes as a single *real* back-slash character.
That's why you need all four: because both the JVM and the regular-expression engine process the string separately, each time chopping it in half. From four to two to one.