Java replaceAll() method

Question

I am trying to understand this piece of codes:

for (File f : files) {
     fileName = f.getName().toUpperCase().replaceAll("_\\d\\d\\d\\d_\\d\\d_\\d\\d_\\d\\d_\\d\\d", "");

     if (fileName.equals(tableName + ".XML")) {
         returnFile = f;
         break;
     }
}

and I am stuck at this part: replaceAll("_\\d\\d\\d\\d_\\d\\d_\\d\\d_\\d\\d_\\d\\d", "")

as far as I know it is trying to remove something from the name (maybe the underscore "_" ) but what exactly is _\\d\\d\\d\\d_\\d\\d_\\d\\d_\\d\\d_\\d\\d

Can somebody please explain?

Learn about regexes.

SLaks
– SLaks

2016-03-30 21:45:47 +00:00
Commented Mar 30, 2016 at 21:45 — SLaks
– SLaks, Commented Mar 30, 2016 at 21:45
This code now has two problems.

user1531971
– user1531971

2016-03-30 21:52:32 +00:00
Commented Mar 30, 2016 at 21:52 — user1531971
– user1531971, Commented Mar 30, 2016 at 21:52
@jdv what are those two problems you are seeing?

Ronaldinho Learn Coding
– Ronaldinho Learn Coding

2016-03-30 22:39:01 +00:00
Commented Mar 30, 2016 at 22:39 — Ronaldinho Learn Coding
– Ronaldinho Learn Coding, Commented Mar 30, 2016 at 22:39
blog.codinghorror.com/…

user1531971
– user1531971

2016-03-30 22:41:55 +00:00
Commented Mar 30, 2016 at 22:41 — user1531971
– user1531971, Commented Mar 30, 2016 at 22:41

Sebastian Paaske Tørholm · Accepted Answer · 2016-03-30 21:53:44Z

2

str.replaceAll("_\\d\\d\\d\\d_\\d\\d_\\d\\d_\\d\\d_\\d\\d", "") takes the string str and replaces all matches of the regular expression _\d\d\d\d_\d\d_\d\d_\d\d_\d\d with nothing (i.e. ""). (The reason it is written \\d and not \d is that the \ is escaped.)

In this case, \d means "a digit". So, more than likely, it removes a date/time from the string. For an example, if str is "screenshot_from_stackoverflow_2016_03_30_23_47.jpg", it becomes screenshot_from_stackoverflow.jpg after the replaceAll.

To get a feel for regular expressions, how they work and what they can do, I would recommend reading up on them, for instance on regular-expressions.info. It has a pretty comprehensive tutorial available.

edited Mar 30, 2016 at 21:53

answered Mar 30, 2016 at 21:48

Sebastian Paaske Tørholm

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3 Comments

ninja.coder Over a year ago

Actually, it will become SCREENSHOT_FROM_STACKOVERFLOW.JPG as he is also doing toUpperCase() before replaceAll().

Sebastian Paaske Tørholm Over a year ago

@user2004685 In the example provided in the question, yes. :) This answer only really covers the replaceAll-part, as it was the part being asked about.

ninja.coder Over a year ago

I'm not correcting you. Just saying for common understand if anyone is interested. :)

ninja.coder · Accepted Answer · 2016-03-30 21:46:46Z

1

as far as I know it is trying to remove something from the name (maybe the underscore "_" ) but what exactly is \d\d\d\d\d\d_\d\d_\d\d_\d\d

It is the pattern which will match the digits [0-9] in this format _XXXX_XX_XX_XX_ and replace it with "" i.e. nothing.

For Example,

_7686_77_78_77_77
_0123_65_58_56_12

Will be replaced in your string with "".

answered Mar 30, 2016 at 21:46

ninja.coder

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Comments

K139 · Accepted Answer · 2016-03-30 21:47:48Z

1

\d - matches a digit [0-9]

Java RegEx

answered Mar 30, 2016 at 21:47

K139

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