Properties File Not Stored In Correct Order

Question

I'm saving several values in a properties file, yet whenever I open the file, the values are not written in the order that I coded.

save.setProperty("SN", "foo");
save.setProperty("ID", "bar");
save.setProperty("TN", "example");
save.setProperty("TC", "generic");
save.setProperty("SW", "incorrect");
save.setProperty("NW", "order");
save.store(new FileOutputStream(file.getAbsolutePath(), null);

This is how the file looks when I open it:

#Sat Jul 13 19:28:59 EDT 2013
ID=bar
SW=incorrect
TC=generic
TN=example
NW=order
SN=foo

As you can see, the order is completely off from the coding. I am curious as to why this happens. It is obviously not sorted alphabetically, and I can't see any other reason why it should happen like this.

You will also notice that comments get moved or removed as well. — user207421, Jul 13 '13 at 23:58
Because if you have a dependency on the order you probably have a conceptual problem with your design. — Hot Licks, Jul 14 '13 at 14:24
@HotLicks I said I was _curious_, didn't I? I don't think I ever said I have a dependency on the order. — Aaron, Jul 14 '13 at 14:51

score 5 · Accepted Answer · edited May 23 '17 at 12:11

5

The Properties class extends the Hashtable class.

The iteration order of a hash-based set is undefined.

Incidentally, the fact that Properties extends Hashtable, instead of using Hashtable, is considered one of the many design "mistakes" in the JDK.

For a brief list of other "mistakes", see this answer.

edited May 23 '17 at 12:11

Community

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answered Jul 13 '13 at 23:48

Bohemian

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score 1 · Answer 2 · answered Jul 13 '13 at 23:42

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There's a good chance that the properties system is using a backing HashMap of some description. This is so that you can set the same property many times over and it will update the current value. To do this efficiently, a HashMap is required. Because of this, the order is entirely up to the implementation of the HashMap (It's not guaranteed to be alphabetical)

answered Jul 13 '13 at 23:42

AStupidNoob

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There's more than a 'good chance'. Properties extends Hashtable. – user207421 Jul 14 '13 at 00:00
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I wasn't 100% certain, I've never used `Properties` before. It was just a guess that turned out to be right! – AStupidNoob Jul 14 '13 at 00:08

Properties File Not Stored In Correct Order

2 Answers2