[SPARK-9534] [BUILD] Enable javac lint for scalac parity; fix a lot of build warnings, 1.5.0 edition

Enable most javac lint warnings; fix a lot of build warnings. In a few cases, touch up surrounding code in the process.

I'll explain several of the changes inline in comments.

Author: Sean Owen <sowen@cloudera.com>

Closes #7862 from srowen/SPARK-9534 and squashes the following commits:

ea51618 [Sean Owen] Enable most javac lint warnings; fix a lot of build warnings. In a few cases, touch up surrounding code in the process.

1 files changed, 11 insertions, 8 deletions

diff --git a/core/src/main/java/org/apache/spark/api/java/JavaSparkContextVarargsWorkaround.java b/core/src/main/java/org/apache/spark/api/java/JavaSparkContextVarargsWorkaround.java
index 2090efd3b9..d4c42b38ac 100644
--- a/core/src/main/java/org/apache/spark/api/java/JavaSparkContextVarargsWorkaround.java
+++ b/core/src/main/java/org/apache/spark/api/java/JavaSparkContextVarargsWorkaround.java
@@ -23,11 +23,13 @@ import java.util.List;
 // See
 // http://scala-programming-language.1934581.n4.nabble.com/Workaround-for-implementing-java-varargs-in-2-7-2-final-tp1944767p1944772.html
 abstract class JavaSparkContextVarargsWorkaround {
-  public <T> JavaRDD<T> union(JavaRDD<T>... rdds) {
+
+  @SafeVarargs
+  public final <T> JavaRDD<T> union(JavaRDD<T>... rdds) {
     if (rdds.length == 0) {
       throw new IllegalArgumentException("Union called on empty list");
     }
-    ArrayList<JavaRDD<T>> rest = new ArrayList<JavaRDD<T>>(rdds.length - 1);
+    List<JavaRDD<T>> rest = new ArrayList<>(rdds.length - 1);
     for (int i = 1; i < rdds.length; i++) {
       rest.add(rdds[i]);
     }
@@ -38,18 +40,19 @@ abstract class JavaSparkContextVarargsWorkaround {
     if (rdds.length == 0) {
       throw new IllegalArgumentException("Union called on empty list");
     }
-    ArrayList<JavaDoubleRDD> rest = new ArrayList<JavaDoubleRDD>(rdds.length - 1);
+    List<JavaDoubleRDD> rest = new ArrayList<>(rdds.length - 1);
     for (int i = 1; i < rdds.length; i++) {
       rest.add(rdds[i]);
     }
     return union(rdds[0], rest);
   }
 
-  public <K, V> JavaPairRDD<K, V> union(JavaPairRDD<K, V>... rdds) {
+  @SafeVarargs
+  public final <K, V> JavaPairRDD<K, V> union(JavaPairRDD<K, V>... rdds) {
     if (rdds.length == 0) {
       throw new IllegalArgumentException("Union called on empty list");
     }
-    ArrayList<JavaPairRDD<K, V>> rest = new ArrayList<JavaPairRDD<K, V>>(rdds.length - 1);
+    List<JavaPairRDD<K, V>> rest = new ArrayList<>(rdds.length - 1);
     for (int i = 1; i < rdds.length; i++) {
       rest.add(rdds[i]);
     }
@@ -57,7 +60,7 @@ abstract class JavaSparkContextVarargsWorkaround {
   }
 
   // These methods take separate "first" and "rest" elements to avoid having the same type erasure
-  abstract public <T> JavaRDD<T> union(JavaRDD<T> first, List<JavaRDD<T>> rest);
-  abstract public JavaDoubleRDD union(JavaDoubleRDD first, List<JavaDoubleRDD> rest);
-  abstract public <K, V> JavaPairRDD<K, V> union(JavaPairRDD<K, V> first, List<JavaPairRDD<K, V>> rest);
+  public abstract <T> JavaRDD<T> union(JavaRDD<T> first, List<JavaRDD<T>> rest);
+  public abstract JavaDoubleRDD union(JavaDoubleRDD first, List<JavaDoubleRDD> rest);
+  public abstract <K, V> JavaPairRDD<K, V> union(JavaPairRDD<K, V> first, List<JavaPairRDD<K, V>> rest);
 }