## What changes were proposed in this pull request?

This PR fixes typos in comments and testcase name of code.

## How was this patch tested?

manual.

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #11481 from dongjoon-hyun/minor_fix_typos_in_code.

## What changes were proposed in this pull request?

After SPARK-6990, `dev/lint-java` keeps Java code healthy and helps PR review by saving much time.
This issue aims remove unused imports from Java/Scala code and add `UnusedImports` checkstyle rule to help developers.

## How was this patch tested?
```
./dev/lint-java
./build/sbt compile
```

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #11438 from dongjoon-hyun/SPARK-13583.

## What changes were proposed in this pull request?

Make some cross-cutting code improvements according to static analysis. These are individually up for discussion since they exist in separate commits that can be reverted. The changes are broadly:

- Inner class should be static
- Mismatched hashCode/equals
- Overflow in compareTo
- Unchecked warnings
- Misuse of assert, vs junit.assert
- get(a) + getOrElse(b) -> getOrElse(a,b)
- Array/String .size -> .length (occasionally, -> .isEmpty / .nonEmpty) to avoid implicit conversions
- Dead code
- tailrec
- exists(_ == ) -> contains find + nonEmpty -> exists filter + size -> count
- reduce(_+_) -> sum map + flatten -> map

The most controversial may be .size -> .length simply because of its size. It is intended to avoid implicits that might be expensive in some places.

## How was the this patch tested?

Existing Jenkins unit tests.

Author: Sean Owen <sowen@cloudera.com>

Closes #11292 from srowen/SPARK-13423.

## What changes were proposed in this pull request?

This PR tries to fix all typos in all markdown files under `docs` module,
and fixes similar typos in other comments, too.

## How was the this patch tested?

manual tests.

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #11300 from dongjoon-hyun/minor_fix_typos.

jegonzal ankurdave please could you review

## What changes were proposed in this pull request?

Reworking of jegonzal PR #2495 to address the issue identified in SPARK-3650. Code amended to use the convertToCanonicalEdges method.

## How was the this patch tested?

Patch was tested using the unit tests created in PR #2495

Author: Robin East <robin.east@xense.co.uk>
Author: Joseph E. Gonzalez <joseph.e.gonzalez@gmail.com>

Closes #11290 from insidedctm/spark-3650.

JIRA: https://issues.apache.org/jira/browse/SPARK-13416

## What changes were proposed in this pull request?

The output of StronglyConnectedComponents with numIter no greater than 1 may make no sense. So I just add require check in it.

## How was the this patch tested?

 unit tests passed

Author: Zheng RuiFeng <ruifengz@foxmail.com>

Closes #11284 from zhengruifeng/scccheck.

JIRA: https://issues.apache.org/jira/browse/SPARK-13386

## What changes were proposed in this pull request?

add maxIteration option for ConnectedComponents algorithm

## How was the this patch tested?

unit tests passed

Author: Zheng RuiFeng <ruifengz@foxmail.com>

Closes #11268 from zhengruifeng/ccwithmax.

Author: Takeshi YAMAMURO <linguin.m.s@gmail.com>

Closes #10918 from maropu/RemoveDeprecateInPregel.

This patch changes Spark's build to make Scala 2.11 the default Scala version. To be clear, this does not mean that Spark will stop supporting Scala 2.10: users will still be able to compile Spark for Scala 2.10 by following the instructions on the "Building Spark" page; however, it does mean that Scala 2.11 will be the default Scala version used by our CI builds (including pull request builds).

The Scala 2.11 compiler is faster than 2.10, so I think we'll be able to look forward to a slight speedup in our CI builds (it looks like it's about 2X faster for the Maven compile-only builds, for instance).

After this patch is merged, I'll update Jenkins to add new compile-only jobs to ensure that Scala 2.10 compilation doesn't break.

Author: Josh Rosen <joshrosen@databricks.com>

Closes #10608 from JoshRosen/SPARK-6363.

Some VertexRDD and EdgeRDD are created during the intermediate step of g.connectedComponents() but unnecessarily left cached after the method is done. The fix is to unpersist these RDDs once they are no longer in use.

A test case is added to confirm the fix for the reported bug.

Author: Jason Lee <cjlee@us.ibm.com>

Closes #10713 from jasoncl/SPARK-12655.

Fix the style violation (space before `,` and `:`).
This PR is a followup for #10643.

Author: Kousuke Saruta <sarutak@oss.nttdata.co.jp>

Closes #10683 from sarutak/SPARK-12692-followup-graphx.

[SPARK-12665][CORE][GRAPHX] Remove Vector, VectorSuite and GraphKryoRegistrator which are deprecated and no longer used

Whole code of Vector.scala, VectorSuite.scala and GraphKryoRegistrator.scala  are no longer used so it's time to remove them in Spark 2.0.

Author: Kousuke Saruta <sarutak@oss.nttdata.co.jp>

Closes #10613 from sarutak/SPARK-12665.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #10582 from vanzin/SPARK-3873-tests.

There's one warning left, caused by a bug in the checker.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #10537 from vanzin/SPARK-3873-graphx.

Author: Takeshi YAMAMURO <linguin.m.s@gmail.com>

Closes #4674 from maropu/AddGraphLoaderSuite.

Author: Reynold Xin <rxin@databricks.com>

Closes #10387 from rxin/version-bump.

We should upgrade to SBT 0.13.9, since this is a requirement in order to use SBT's new Maven-style resolution features (which will be done in a separate patch, because it's blocked by some binary compatibility issues in the POM reader plugin).

I also upgraded Scalastyle to version 0.8.0, which was necessary in order to fix a Scala 2.10.5 compatibility issue (see https://github.com/scalastyle/scalastyle/issues/156). The newer Scalastyle is slightly stricter about whitespace surrounding tokens, so I fixed the new style violations.

Author: Josh Rosen <joshrosen@databricks.com>

Closes #10112 from JoshRosen/upgrade-to-sbt-0.13.9.

The code convertToCanonicalEdges is such that srcIds are smaller than dstIds but the scaladoc suggested otherwise. Have fixed the same.

Author: Gaurav Kumar <gauravkumar37@gmail.com>

Closes #9666 from gauravkumar37/patch-1.

This patch modifies Spark's closure cleaner (and a few other places) to use ASM 5, which is necessary in order to support cleaning of closures that were compiled by Java 8.

In order to avoid ASM dependency conflicts, Spark excludes ASM from all of its dependencies and uses a shaded version of ASM 4 that comes from `reflectasm` (see [SPARK-782](https://issues.apache.org/jira/browse/SPARK-782) and #232). This patch updates Spark to use a shaded version of ASM 5.0.4 that was published by the Apache XBean project; the POM used to create the shaded artifact can be found at https://github.com/apache/geronimo-xbean/blob/xbean-4.4/xbean-asm5-shaded/pom.xml.

http://movingfulcrum.tumblr.com/post/80826553604/asm-framework-50-the-missing-migration-guide was a useful resource while upgrading the code to use the new ASM5 opcodes.

I also added a new regression tests in the `java8-tests` subproject; the existing tests were insufficient to catch this bug, which only affected Scala 2.11 user code which was compiled targeting Java 8.

Author: Josh Rosen <joshrosen@databricks.com>

Closes #9512 from JoshRosen/SPARK-6152.

Changes the personalized pagerank initialization to be non-uniform.

Author: Yves Raimond <yraimond@netflix.com>

Closes #9386 from moustaki/personalized-pagerank-init.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #8775 from vanzin/SPARK-10300.

Author: Reynold Xin <rxin@databricks.com>

Closes #8350 from rxin/1.6.

Comments preceding toMessage method state: "The edge partition is encoded in the lower
   * 30 bytes of the Int, and the position is encoded in the upper 2 bytes of the Int.". References to bytes should be changed to bits.

This contribution is my original work and I license the work to the Spark project under it's open source license.

Author: Robin East <robin.east@xense.co.uk>

Closes #8756 from insidedctm/master.

Move .java files in `src/main/scala` to `src/main/java` root, except for `package-info.java` (to stay next to package.scala)

Author: Sean Owen <sowen@cloudera.com>

Closes #8736 from srowen/SPARK-10576.

The bulk of the changes are on `transient` annotation on class parameter. Often the compiler doesn't generate a field for this parameters, so the the transient annotation would be unnecessary.
But if the class parameter are used in methods, then fields are created. So it is safer to keep the annotations.

The remainder are some potential bugs, and deprecated syntax.

Author: Luc Bourlier <luc.bourlier@typesafe.com>

Closes #8433 from skyluc/issue/sbt-2.11.

Author: zc he <farseer90718@gmail.com>

Closes #8188 from farseer90718/farseer-patch-1.

SPARK-3190 was originally fixed by 96df9290, but a5ef5811 introduced a regression during refactoring. This commit fixes the regression.

Author: Ankur Dave <ankurdave@gmail.com>

Closes #7923 from ankurdave/SPARK-3190-reopening and squashes the following commits:

a3e1b23 [Ankur Dave] Fix VertexRDD.count() overflow regression

Pregel code contains two consecutive joins:
```
g.vertices.innerJoin(messages)(vprog)
...
g = g.outerJoinVertices(newVerts)
{ (vid, old, newOpt) => newOpt.getOrElse(old) }
```
This can be simplified with one join. ankurdave proposed a patch based on our discussion in the mailing list: https://www.mail-archive.com/devspark.apache.org/msg10316.html

Author: Alexander Ulanov <nashb@yandex.ru>

Closes #7749 from avulanov/SPARK-9436-pregel and squashes the following commits:

8568e06 [Alexander Ulanov] Pregel simplification patch

The change here is to keep the cached RDDs in the graph object so that when the graph.unpersist() is called these RDDs are correctly unpersisted.

```java
import org.apache.spark.graphx._
import org.apache.spark.rdd.RDD
import org.slf4j.LoggerFactory
import org.apache.spark.graphx.util.GraphGenerators

// Create an RDD for the vertices
val users: RDD[(VertexId, (String, String))] =
  sc.parallelize(Array((3L, ("rxin", "student")), (7L, ("jgonzal", "postdoc")),
                       (5L, ("franklin", "prof")), (2L, ("istoica", "prof"))))
// Create an RDD for edges
val relationships: RDD[Edge[String]] =
  sc.parallelize(Array(Edge(3L, 7L, "collab"),    Edge(5L, 3L, "advisor"),
                       Edge(2L, 5L, "colleague"), Edge(5L, 7L, "pi")))
// Define a default user in case there are relationship with missing user
val defaultUser = ("John Doe", "Missing")
// Build the initial Graph
val graph = Graph(users, relationships, defaultUser)
graph.cache().numEdges

graph.unpersist()

sc.getPersistentRDDs.foreach( r => println( r._2.toString))
```

Author: tien-dungle <tien-dung.le@realimpactanalytics.com>

Closes #7469 from tien-dungle/SPARK-9109_Graphx-unpersist and squashes the following commits:

8d87997 [tien-dungle] Keep the cached edge in the graph

This pull request adds a Scalastyle regex rule which fails the style check if `Class.forName` is used directly.  `Class.forName` always loads classes from the default / system classloader, but in a majority of cases, we should be using Spark's own `Utils.classForName` instead, which tries to load classes from the current thread's context classloader and falls back to the classloader which loaded Spark when the context classloader is not defined.

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Author: Josh Rosen <joshrosen@databricks.com>

Closes #7350 from JoshRosen/ban-Class.forName and squashes the following commits:

e3e96f7 [Josh Rosen] Merge remote-tracking branch 'origin/master' into ban-Class.forName
c0b7885 [Josh Rosen] Hopefully fix the last two cases
d707ba7 [Josh Rosen] Fix uses of Class.forName that I missed in my first cleanup pass
046470d [Josh Rosen] Merge remote-tracking branch 'origin/master' into ban-Class.forName
62882ee [Josh Rosen] Fix uses of Class.forName or add exclusion.
d9abade [Josh Rosen] Add stylechecker rule to ban uses of Class.forName

See https://github.com/aray/e2d/blob/master/EdgePartition2D.ipynb

Author: Andrew Ray <ray.andrew@gmail.com>

Closes #7104 from aray/edge-partition-2d-improvement and squashes the following commits:

3729f84 [Andrew Ray] correct bounds and remove unneeded comments
97f8464 [Andrew Ray] change less
5141ab4 [Andrew Ray] Merge branch 'master' into edge-partition-2d-improvement
925fd2c [Andrew Ray] use new interface for partitioning
001bfd0 [Andrew Ray] Refactor PartitionStrategy so that we can return a prtition function for a given number of parts. To keep compatibility we define default methods that translate between the two implementation options. Made EdgePartition2D use old strategy when we have a perfect square and implement new interface.
5d42105 [Andrew Ray] % -> /
3560084 [Andrew Ray] Merge branch 'master' into edge-partition-2d-improvement
f006364 [Andrew Ray] remove unneeded comments
cfa2c5e [Andrew Ray] Modifications to EdgePartition2D so that it works for non perfect squares.

Author: Jonathan Alter <jonalter@users.noreply.github.com>

Closes #7093 from jonalter/SPARK-7977 and squashes the following commits:

ccd44cc [Jonathan Alter] Changed println to log in ThreadingSuite
7fcac3e [Jonathan Alter] Reverting to println in ThreadingSuite
10724b6 [Jonathan Alter] Changing some printlns to logs in tests
eeec1e7 [Jonathan Alter] Merge branch 'master' of github.com:apache/spark into SPARK-7977
0b1dcb4 [Jonathan Alter] More println cleanup
aedaf80 [Jonathan Alter] Merge branch 'master' of github.com:apache/spark into SPARK-7977
925fd98 [Jonathan Alter] Merge branch 'master' of github.com:apache/spark into SPARK-7977
0c16fa3 [Jonathan Alter] Replacing some printlns with logs
45c7e05 [Jonathan Alter] Merge branch 'master' of github.com:apache/spark into SPARK-7977
5c8e283 [Jonathan Alter] Allowing println in audit-release examples
5b50da1 [Jonathan Alter] Allowing printlns in example files
ca4b477 [Jonathan Alter] Merge branch 'master' of github.com:apache/spark into SPARK-7977
83ab635 [Jonathan Alter] Fixing new printlns
54b131f [Jonathan Alter] Merge branch 'master' of github.com:apache/spark into SPARK-7977
1cd8a81 [Jonathan Alter] Removing some unnecessary comments and printlns
b837c3a [Jonathan Alter] Disallowing println

Author: Patrick Wendell <patrick@databricks.com>

Closes #6328 from pwendell/spark-1.5-update and squashes the following commits:

2f42d02 [Patrick Wendell] A few more excludes
4bebcf0 [Patrick Wendell] Update to RC4
61aaf46 [Patrick Wendell] Using new release candidate
55f1610 [Patrick Wendell] Another exclude
04b4f04 [Patrick Wendell] More issues with transient 1.4 changes
36f549b [Patrick Wendell] [SPARK-7801] [BUILD] Updating versions to SPARK 1.5.0

Author: Reynold Xin <rxin@databricks.com>

Closes #6536 from rxin/structural-type-checker and squashes the following commits:

f833151 [Reynold Xin] Fixed compilation.
633f9a1 [Reynold Xin] Fixed typo.
d1fa804 [Reynold Xin] [SPARK-7979] Enforce structural type checker.

Author: Reynold Xin <rxin@databricks.com>

Closes #6530 from rxin/trim-whitespace-1 and squashes the following commits:

7b7b3a0 [Reynold Xin] Reset again.
dc14597 [Reynold Xin] Reset scalastyle.
cd556c4 [Reynold Xin] YARN, Kinesis, Flume.
4223fe1 [Reynold Xin] [SPARK-3850] Trim trailing spaces for examples/streaming.

Right now `unit-tests.log` are not of much value because we can't tell where the test boundaries are easily. This patch adds log statements before and after each test to outline the test boundaries, e.g.:

```
===== TEST OUTPUT FOR o.a.s.serializer.KryoSerializerSuite: 'kryo with parallelize for primitive arrays' =====

15/05/27 12:36:39.596 pool-1-thread-1-ScalaTest-running-KryoSerializerSuite INFO SparkContext: Starting job: count at KryoSerializerSuite.scala:230
15/05/27 12:36:39.596 dag-scheduler-event-loop INFO DAGScheduler: Got job 3 (count at KryoSerializerSuite.scala:230) with 4 output partitions (allowLocal=false)
15/05/27 12:36:39.596 dag-scheduler-event-loop INFO DAGScheduler: Final stage: ResultStage 3(count at KryoSerializerSuite.scala:230)
15/05/27 12:36:39.596 dag-scheduler-event-loop INFO DAGScheduler: Parents of final stage: List()
15/05/27 12:36:39.597 dag-scheduler-event-loop INFO DAGScheduler: Missing parents: List()
15/05/27 12:36:39.597 dag-scheduler-event-loop INFO DAGScheduler: Submitting ResultStage 3 (ParallelCollectionRDD[5] at parallelize at KryoSerializerSuite.scala:230), which has no missing parents

...

15/05/27 12:36:39.624 pool-1-thread-1-ScalaTest-running-KryoSerializerSuite INFO DAGScheduler: Job 3 finished: count at KryoSerializerSuite.scala:230, took 0.028563 s
15/05/27 12:36:39.625 pool-1-thread-1-ScalaTest-running-KryoSerializerSuite INFO KryoSerializerSuite:

***** FINISHED o.a.s.serializer.KryoSerializerSuite: 'kryo with parallelize for primitive arrays' *****

...
```

Author: Andrew Or <andrew@databricks.com>

Closes #6441 from andrewor14/demarcate-tests and squashes the following commits:

879b060 [Andrew Or] Fix compile after rebase
d622af7 [Andrew Or] Merge branch 'master' of github.com:apache/spark into demarcate-tests
017c8ba [Andrew Or] Merge branch 'master' of github.com:apache/spark into demarcate-tests
7790b6c [Andrew Or] Fix tests after logical merge conflict
c7460c0 [Andrew Or] Merge branch 'master' of github.com:apache/spark into demarcate-tests
c43ffc4 [Andrew Or] Fix tests?
8882581 [Andrew Or] Fix tests
ee22cda [Andrew Or] Fix log message
fa9450e [Andrew Or] Merge branch 'master' of github.com:apache/spark into demarcate-tests
12d1e1b [Andrew Or] Various whitespace changes (minor)
69cbb24 [Andrew Or] Make all test suites extend SparkFunSuite instead of FunSuite
bbce12e [Andrew Or] Fix manual things that cannot be covered through automation
da0b12f [Andrew Or] Add core tests as dependencies in all modules
f7d29ce [Andrew Or] Introduce base abstract class for all test suites

So we can enable a whitespace enforcement rule in the style checker to save code review time.

Author: Reynold Xin <rxin@databricks.com>

Closes #6474 from rxin/whitespace-graphx and squashes the following commits:

4d3cd26 [Reynold Xin] Fixed tests.
869dde4 [Reynold Xin] [SPARK-7927] whitespace fixes for GraphX.

Here's a modification to PageRank which does personalized PageRank.  The approach is basically similar to that outlined by Bahmani et al. from 2010 (http://arxiv.org/pdf/1006.2880.pdf).

I'm sure this needs tuning up or other considerations, so let me know how I can improve this.

Author: Dan McClary <dan.mcclary@gmail.com>
Author: dwmclary <dan.mcclary@gmail.com>

Closes #4774 from dwmclary/SPARK-5854-Personalized-PageRank and squashes the following commits:

8b907db [dwmclary] fixed scalastyle errors in PageRankSuite
2c20e5d [dwmclary] merged with upstream master
d6cebac [dwmclary] updated as per style requests
7d00c23 [Dan McClary] fixed line overrun in personalizedVertexPageRank
d711677 [Dan McClary] updated vertexProgram to restore binary compatibility for inner method
bb8d507 [Dan McClary] Merge branch 'master' of https://github.com/apache/spark into SPARK-5854-Personalized-PageRank
fba0edd [Dan McClary] fixed silly mistakes
de51be2 [Dan McClary] cleaned up whitespace between comments and methods
0c30d0c [Dan McClary] updated to maintain binary compatibility
aaf0b4b [Dan McClary] Merge branch 'master' of https://github.com/apache/spark into SPARK-5854-Personalized-PageRank
76773f6 [Dan McClary] Merge branch 'master' of https://github.com/apache/spark into SPARK-5854-Personalized-PageRank
44ada8e [Dan McClary] updated tolerance on chain PPR
1ffed95 [Dan McClary] updated tolerance on chain PPR
b67ac69 [Dan McClary] updated tolerance on chain PPR
a560942 [Dan McClary] rolled PPR into pregel code for PageRank
6dc2c29 [Dan McClary] initial implementation of personalized page rank

Author: Michael Malak <michaelmalak@yahoo.com>

Closes #5464 from michaelmalak/master and squashes the following commits:

9d942ba [Michael Malak] SPARK-6710 GraphX Fixed Wrong initial bias in GraphX SVDPlusPlus

https://issues.apache.org/jira/browse/SPARK-6758

I am not sure if it is ok to block them in test resources too (as we shade jetty in assembly?).

Author: WangTaoTheTonic <wangtao111@huawei.com>

Closes #5406 from WangTaoTheTonic/SPARK-6758 and squashes the following commits:

e09605b [WangTaoTheTonic] block the right jetty package