Why do Java libraries use constant ints more than enums?

Question

I am not sure if this is a definitive statement, but it seems to me that the Java API prefers constant ints over enums. From the parts of the API that I have used, I've encountered many final static int constants where an enum could have been used instead. Once such example that I happen to be staring at this moment:

From java.awt.BasicStroke:

public final static int CAP_BUTT = 0;
public final static int CAP_ROUND = 1;
public final static int CAP_SQUARE = 2;

In fact, I don't think I've ever seen an enum used in a standard Java API class. Why is this?

I'm designing an API for my own application (about a billion times smaller than the Java API, but I'm still trying to be smart about it), and trying to decide whether to use constant ints or enums. THIS post references a very popular book I haven't read yet which implies enums have many advantages. Most other highly scored answers in that same thread agree. So why does Java not seem to use its own enum capabilities?

One guess just popped into my mind right after posting. Maybe `enum` wasn't available in Java a long time ago when all these classes were designed? — The111, Feb 23 '13 at 23:53
It's probably code that was written before the language had enums. As it's a public API it cannot be changed — James, Feb 23 '13 at 23:54
@Reimeus post it as an answer with a link to `enum` javadoc. — Luiggi Mendoza, Feb 23 '13 at 23:55
Well that was a quick answer. :-) Reimeus gets the answer if he posts it. — The111, Feb 23 '13 at 23:56

Reimeus · Accepted Answer · 2013-02-24T00:11:43.233

13

BasicStroke pre-dates enum which arrived in Java 1.5. The code has been left as-is for backward compatibility. When writing any new code, enums are definitely a better design choice over final static variables.

edited Feb 24 '13 at 00:11

answered Feb 23 '13 at 23:57

Reimeus

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score 11 · Answer 2 · answered Feb 23 '13 at 23:55

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It's nothing to do with constant int being better than an enum: it's just that enum was only added in JDK 5, so most of the java API was written before enum was available: constant ints were the only option, so were used.

If the java API was re-written it would include far more enums, and you can expect to see them appear in new additions to the API in JDK6 or later.

You should probably use enums for your application, they are generally the better option.

answered Feb 23 '13 at 23:55

Jon Story

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Thanks Jon, you'd get the answer if Reimeus hadn't posted his comment first. ;-) Good info here too. – The111 Feb 24 '13 at 00:10
Did he? My screen says mine was 16 mins ago, his was 14. Not that I'm upset :p – Jon Story Feb 24 '13 at 00:12
He posted a `comment` before he posted the `answer`. ;-P I promised him the "accept" if he posted it as an answer, just before I saw your answer come up. Had to go through on my promise... but usually I give the accept to the underdog with the lower overall score. :-) – The111 Feb 24 '13 at 00:14

Why do Java libraries use constant ints more than enums?

2 Answers2