ARROW-1347: [JAVA] Return consistent child field name for List Vectors

This makes the child fields of ListVector have consistent names of `ListVector.DATA_VECTOR_NAME`. Previously, an empty ListVector would have a child name of `ZeroVector.name` which is "[DEFAULT]".

Author: Bryan Cutler <cutlerb@gmail.com>
Author: Steven Phillips <steven@dremio.com>

Closes apache#1119 from BryanCutler/java-ListVector-child-name-ARROW-1347 and squashes the following commits:

c240378 [Bryan Cutler] changed to use instanceof and added test
2923a45 [Steven Phillips] ARROW-1347: [JAVA] return consistent child field name for List vectors

java/vector/src/main/java/org/apache/arrow/vector/complex/ListVector.java

@@ -48,6 +48,7 @@
 import org.apache.arrow.vector.schema.ArrowFieldNode;
 import org.apache.arrow.vector.types.Types.MinorType;
 import org.apache.arrow.vector.types.pojo.ArrowType;
+import org.apache.arrow.vector.types.pojo.ArrowType.Null;
 import org.apache.arrow.vector.types.pojo.DictionaryEncoding;
 import org.apache.arrow.vector.types.pojo.Field;
 import org.apache.arrow.vector.types.pojo.FieldType;
@@ -296,6 +297,9 @@ public int getBufferSize() {
 
  @Override
  public Field getField() {
+ if (getDataVector() instanceof ZeroVector) {
+ return new Field(name, fieldType, ImmutableList.of(new Field(DATA_VECTOR_NAME, FieldType.nullable(Null.INSTANCE), null)));
+ }
  return new Field(name, fieldType, ImmutableList.of(getDataVector().getField()));
  }
 

java/vector/src/test/java/org/apache/arrow/vector/TestListVector.java

@@ -80,4 +80,16 @@ public void testCopyFrom() throws Exception {
  Assert.assertTrue("shouldn't be null", reader.isSet());
  }
  }
+
+ @Test
+ public void testConsistentChildName() throws Exception {
+ try (ListVector listVector = ListVector.empty("sourceVector", allocator)) {
+ String emptyListStr = listVector.getField().toString();
+ assertTrue(emptyListStr.contains(ListVector.DATA_VECTOR_NAME));
+
+ listVector.addOrGetVector(FieldType.nullable(MinorType.INT.getType()));
+ String emptyVectorStr = listVector.getField().toString();
+ assertTrue(emptyVectorStr.contains(ListVector.DATA_VECTOR_NAME));
+ }
+ }
 }