SPARK-5270 [CORE] Provide isEmpty() function in RDD API

Pretty minor, but submitted for consideration -- this would at least help people make this check in the most efficient way I know.

Author: Sean Owen <sowen@cloudera.com>

Closes #4074 from srowen/SPARK-5270 and squashes the following commits:

66885b8 [Sean Owen] Add note that JavaRDDLike should not be implemented by user code
2e9b490 [Sean Owen] More tests, and Mima-exclude the new isEmpty method in JavaRDDLike
28395ff [Sean Owen] Add isEmpty to Java, Python
7dd04b7 [Sean Owen] Add efficient RDD.isEmpty()

1 files changed, 21 insertions, 0 deletions

diff --git a/core/src/test/java/org/apache/spark/JavaAPISuite.java b/core/src/test/java/org/apache/spark/JavaAPISuite.java
index 07b1e44d04..004de05c10 100644
--- a/core/src/test/java/org/apache/spark/JavaAPISuite.java
+++ b/core/src/test/java/org/apache/spark/JavaAPISuite.java
@@ -607,6 +607,27 @@ public class JavaAPISuite implements Serializable {
   }
 
   @Test
+  public void isEmpty() {
+    Assert.assertTrue(sc.emptyRDD().isEmpty());
+    Assert.assertTrue(sc.parallelize(new ArrayList<Integer>()).isEmpty());
+    Assert.assertFalse(sc.parallelize(Arrays.asList(1)).isEmpty());
+    Assert.assertTrue(sc.parallelize(Arrays.asList(1, 2, 3), 3).filter(
+        new Function<Integer,Boolean>() {
+          @Override
+          public Boolean call(Integer i) {
+            return i < 0;
+          }
+        }).isEmpty());
+    Assert.assertFalse(sc.parallelize(Arrays.asList(1, 2, 3)).filter(
+        new Function<Integer, Boolean>() {
+          @Override
+          public Boolean call(Integer i) {
+            return i > 1;
+          }
+        }).isEmpty());
+  }
+
+  @Test
   public void cartesian() {
     JavaDoubleRDD doubleRDD = sc.parallelizeDoubles(Arrays.asList(1.0, 1.0, 2.0, 3.0, 5.0, 8.0));
     JavaRDD<String> stringRDD = sc.parallelize(Arrays.asList("Hello", "World"));