[SPARK-10778][MLlib]Implement toString for AssociationRules.Rule

[y-shimizu]

I implemented toString for AssociationRules.Rule, format like [x, y] => {z}: 1.0

[srowen]

Trivial, but you should use @return and there's no need to state the return type again. Remove the blank line below too

[y-shimizu]

@srowen
Thank you for review.
I fixed.

[mengxr]

Actually, I think Returns is better than @return. If we use @return, the message doesn't show up by default in the API doc, e.g.,

User needs to open it to see the doc:

If we use Returns, it shows up by default:

@srowen

[srowen]

Sure, I don't feel strongly about it. Wouldn't this argument go for all return docs though? They're hidden by default for brevity. Maybe important ones should be put inline in the main doc but toString seems pretty minor.

[mengxr]

For each method, there should be a summary sentence at the beginning, which shows up in the API doc by default. Other details are hidden by default. I think this is Scala specific. You can find the official guide at http://docs.scala-lang.org/style/scaladoc.html:

If the documentation of a method is a one line description of
what that method returns, do not repeat it with an @return annotation.

[y-shimizu]

@mengxr I fixed format.

So, which should I use, Returns or @return ?

[mengxr]

Returns. For toString, it is also okay to remove the JavaDoc entirely.

[y-shimizu]

@mengxr I fixed.

[SparkQA]

Test build #1815 has finished for PR 8904 at commit 1f9ce43.

• This patch fails Scala style tests.
• This patch merges cleanly.
• This patch adds no public classes.

[srowen]

We still need a return type on the method, and the line is too long and needs to be wrapped

[y-shimizu]

@srowen I fixed.

[SparkQA]

Test build #1816 has finished for PR 8904 at commit ae12fba.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #1817 has finished for PR 8904 at commit ae12fba.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #1819 has finished for PR 8904 at commit ae12fba.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[srowen]

Merged to master