[SPARK-6268][MLlib] KMeans parameter getter methods

[hhbyyh]

jira: https://issues.apache.org/jira/browse/SPARK-6268

KMeans has many setters for parameters. It should have matching getters.

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Test build #28460 has started for PR 4974 at commit f94a3d7.

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Test build #28460 has finished for PR 4974 at commit f94a3d7.

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[mengxr]

setRuns is an experimental API, so it should be the same for getRuns.

[mengxr]

LGTM except one minor inline comment.

[SparkQA]

Test build #28466 has started for PR 4974 at commit f44d4dc.

• This patch merges cleanly.

[hhbyyh]

@mengxr Thanks for review. New commit submitted.

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Test build #28466 has finished for PR 4974 at commit f44d4dc.

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• This patch merges cleanly.
• This patch adds no public classes.

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[srowen]

Nit: You could prefix this with @return
Interesting question: naming getters getFoo is of course standard in Java, and seems just fine too, although in Scala we'd be more used to accessing foo only. It's possible to declare private var _foo and then declare the public getter to have name foo here. Does anyone prefer that?

[hhbyyh]

Hi @srowen Thanks for the suggestions.

1. For adding the @return prefix. Sounds fair, and if we're doing it, shall we change other implementations as well? (like LDA, GaussianMixture and others).
2. For using foo rather than getFoo, again it may impact a wide range of code. And shall we change setters to age_= (value:Int) : this.type ? @srowen, @mengxr ,@jkbradley. I'm not sure what's the general recommendation within Spark. And I'd appreciate if there can be a quick decision from community leads. Thanks.

[srowen]

Ignore my second comment; it would take a fair bit more change including changing current setters.
I would not change javadoc on other code, no. LGTM.

[mengxr]

Merged into master. Thanks!