[SPARK-7733] [CORE] [BUILD] Update build, code to use Java 7 for 1.5.0+

Update build to use Java 7, and remove some comments and special-case support for Java 6.

Author: Sean Owen <sowen@cloudera.com>

Closes #6265 from srowen/SPARK-7733 and squashes the following commits:

59bda4e [Sean Owen] Update build to use Java 7, and remove some comments and special-case support for Java 6

3 files changed, 3 insertions, 7 deletions

diff --git a/core/src/main/scala/org/apache/spark/util/MutableURLClassLoader.scala b/core/src/main/scala/org/apache/spark/util/MutableURLClassLoader.scala
index 1e0ba5c287..169489df6c 100644
--- a/core/src/main/scala/org/apache/spark/util/MutableURLClassLoader.scala
+++ b/core/src/main/scala/org/apache/spark/util/MutableURLClassLoader.scala
@@ -52,8 +52,8 @@ private[spark] class ChildFirstURLClassLoader(urls: Array[URL], parent: ClassLoa
    * Used to implement fine-grained class loading locks similar to what is done by Java 7. This
    * prevents deadlock issues when using non-hierarchical class loaders.
    *
-   * Note that due to Java 6 compatibility (and some issues with implementing class loaders in
-   * Scala), Java 7's `ClassLoader.registerAsParallelCapable` method is not called.
+   * Note that due to some issues with implementing class loaders in
+   * Scala, Java 7's `ClassLoader.registerAsParallelCapable` method is not called.
    */
   private val locks = new ConcurrentHashMap[String, Object]()
 
diff --git a/core/src/main/scala/org/apache/spark/util/Utils.scala b/core/src/main/scala/org/apache/spark/util/Utils.scala
index 5f13241054..153ece6224 100644
--- a/core/src/main/scala/org/apache/spark/util/Utils.scala
+++ b/core/src/main/scala/org/apache/spark/util/Utils.scala
@@ -1295,8 +1295,7 @@ private[spark] object Utils extends Logging {
       } catch {
         case t: Throwable =>
           if (originalThrowable != null) {
-            // We could do originalThrowable.addSuppressed(t), but it's
-            // not available in JDK 1.6.
+            originalThrowable.addSuppressed(t)
             logWarning(s"Suppressing exception in finally: " + t.getMessage, t)
             throw originalThrowable
           } else {
diff --git a/core/src/test/scala/org/apache/spark/util/collection/SorterSuite.scala b/core/src/test/scala/org/apache/spark/util/collection/SorterSuite.scala
index 72fd6daba8..b2f5d9009e 100644
--- a/core/src/test/scala/org/apache/spark/util/collection/SorterSuite.scala
+++ b/core/src/test/scala/org/apache/spark/util/collection/SorterSuite.scala
@@ -103,9 +103,6 @@ class SorterSuite extends SparkFunSuite {
    * has the keys and values alternating. The basic Java sorts work only on the keys, so the
    * real Java solution is to make Tuple2s to store the keys and values and sort an array of
    * those, while the Sorter approach can work directly on the input data format.
-   *
-   * Note that the Java implementation varies tremendously between Java 6 and Java 7, when
-   * the Java sort changed from merge sort to TimSort.
    */
   ignore("Sorter benchmark for key-value pairs") {
     val numElements = 25000000 // 25 mil