Hints for java.lang.String.replace problem?

Question

I would like to replace "." by "," in a String/double that I want to write to a file.

Using the following Java code

double myDouble = myObject.getDoubleMethod(); // returns 38.1882352941176
System.out.println(myDouble);

String myDoubleString = "" + myDouble;
System.out.println(myDoubleString);

myDoubleString.replace(".", ",");
System.out.println(myDoubleString);

myDoubleString.replace('.', ',');
System.out.println(myDoubleString);

I get the following output

38.1882352941176
38.1882352941176
38.1882352941176
38.1882352941176

Why isn't replace doing what it is supposed to do? I expect the last two lines to contain a ",".

Do I have to do/use something else? Suggestions?

I have re-read the docs of replace and it clearly starts with "Returns a new string ..." ;-) — CL23, Jul 22 '09 at 17:36

score 20 · Accepted Answer · edited Feb 16 '15 at 18:49

20

You need to assign the new value back to the variable.

double myDouble = myObject.getDoubleMethod(); // returns 38.1882352941176
System.out.println(myDouble);

String myDoubleString = "" + myDouble;
System.out.println(myDoubleString);

myDoubleString = myDoubleString.replace(".", ",");
System.out.println(myDoubleString);

myDoubleString = myDoubleString.replace('.', ',');
System.out.println(myDoubleString);

edited Feb 16 '15 at 18:49

Joe

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answered Jul 22 '09 at 17:30

AlbertoPL

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4

As usual the problem sits in front of the computer ;-) Thx – CL23 Jul 22 '09 at 17:33
6

The reason it returns a new string is that Strings are immutable in Java. – Powerlord Jul 22 '09 at 17:54

score 11 · Answer 2 · edited Jan 08 '15 at 04:09

11

The original String isn't being modified. The call returns the modified string, so you'd need to do this:

String modded = myDoubleString.replace(".",",");
System.out.println( modded );

edited Jan 08 '15 at 04:09

Nishanthi Grashia

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answered Jul 22 '09 at 17:31

Chris Kessel

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score 10 · Answer 3 · edited Sep 29 '14 at 17:07

10

The bigger question is why not use DecimalFormat instead of doing String replace?

edited Sep 29 '14 at 17:07

rink.attendant.6

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answered Jul 22 '09 at 19:46

vh.

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Very good point! Your answer goes beyond my question, but solves the problem that I essentially had. I didn't know DecimalFormat, thanks! – CL23 Jul 22 '09 at 21:16

score 5 · Answer 4 · answered Jul 22 '09 at 17:32

5

replace returns a new String (since String is immutable in Java):

String newString = myDoubleString.replace(".", ",");

answered Jul 22 '09 at 17:32

dfa

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But you need not introduce `newString`, because although `String` objects are immutable, references to `String` objects can be changed (if they are not `final`): http://stackoverflow.com/questions/1552301/immutability-of-strings-in-java – Raedwald Jan 02 '15 at 19:07

score 3 · Answer 5 · answered Jul 22 '09 at 17:49

3

Always remember, Strings are immutable. They can't change. If you're calling a String method that changes it in some way, you need to store the return value. Always.

I remember getting caught out with this more than a few times at Uni :)

answered Jul 22 '09 at 17:49

Brian Beckett

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Hints for java.lang.String.replace problem?

5 Answers5

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