apacheGH-43577: [Java] getBuffers method needs correction on clear fl…

…ag usage (apache#43583)

### Rationale for this change

`getBuffers` method provides the capability to clear the buffers in the vector, this has not been properly tested while clear flag is not properly used in the implementation across various types of vectors. 

### What changes are included in this PR?

Updating the vector `getBuffers` method to use `clear` flag as expected and adding corresponding test cases. 

### Are these changes tested?

Yes, via existing test cases and new test cases. 

### Are there any user-facing changes?

Yes
* GitHub Issue: apache#43577

Authored-by: Vibhatha Abeykoon <[email protected]>
Signed-off-by: David Li <[email protected]>

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

@@ -382,6 +382,17 @@ public VectorWithOrdinal getChildVectorWithOrdinal(String name) {
     return new VectorWithOrdinal(vector, ordinal);
   }
 
+  /**
+   * Return the underlying buffers associated with this vector. Note that this doesn't impact the
+   * reference counts for this buffer, so it only should be used for in-context access. Also note
+   * that this buffer changes regularly, thus external classes shouldn't hold a reference to it
+   * (unless they change it).
+   *
+   * @param clear Whether to clear vector before returning, the buffers will still be refcounted but
+   *     the returned array will be the only reference to them. Also, this won't clear the child
+   *     buffers.
+   * @return The underlying {@link ArrowBuf buffers} that is used by this vector instance.
+   */
   @Override
   public ArrowBuf[] getBuffers(boolean clear) {
     final List<ArrowBuf> buffers = new ArrayList<>();

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

@@ -271,6 +271,17 @@ public void reset() {
     valueCount = 0;
   }
 
+  /**
+   * Return the underlying buffers associated with this vector. Note that this doesn't impact the
+   * reference counts for this buffer, so it only should be used for in-context access. Also note
+   * that this buffer changes regularly, thus external classes shouldn't hold a reference to it
+   * (unless they change it).
+   *
+   * @param clear Whether to clear vector before returning, the buffers will still be refcounted but
+   *     the returned array will be the only reference to them. Also, this won't clear the child
+   *     buffers.
+   * @return The underlying {@link ArrowBuf buffers} that is used by this vector instance.
+   */
   @Override
   public ArrowBuf[] getBuffers(boolean clear) {
     final ArrowBuf[] buffers;

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

@@ -360,6 +360,17 @@ public void reset() {
     valueCount = 0;
   }
 
+  /**
+   * Return the underlying buffers associated with this vector. Note that this doesn't impact the
+   * reference counts for this buffer, so it only should be used for in-context access. Also note
+   * that this buffer changes regularly, thus external classes shouldn't hold a reference to it
+   * (unless they change it).
+   *
+   * @param clear Whether to clear vector before returning, the buffers will still be refcounted but
+   *     the returned array will be the only reference to them. Also, this won't clear the child
+   *     buffers.
+   * @return The underlying {@link ArrowBuf buffers} that is used by this vector instance.
+   */
   @Override
   public ArrowBuf[] getBuffers(boolean clear) {
     setReaderAndWriterIndex();

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

@@ -882,12 +882,13 @@ public void reset() {
 
   /**
    * Return the underlying buffers associated with this vector. Note that this doesn't impact the
-   * reference counts for this buffer so it only should be used for in-context access. Also note
-   * that this buffer changes regularly thus external classes shouldn't hold a reference to it
+   * reference counts for this buffer, so it only should be used for in-context access. Also note
+   * that this buffer changes regularly, thus external classes shouldn't hold a reference to it
    * (unless they change it).
    *
-   * @param clear Whether to clear vector before returning; the buffers will still be refcounted but
-   *     the returned array will be the only reference to them
+   * @param clear Whether to clear vector before returning, the buffers will still be refcounted but
+   *     the returned array will be the only reference to them. Also, this won't clear the child
+   *     buffers.
    * @return The underlying {@link ArrowBuf buffers} that is used by this vector instance.
    */
   @Override

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

@@ -546,7 +546,8 @@ public void reset() {
    * (unless they change it).
    *
    * @param clear Whether to clear vector before returning, the buffers will still be refcounted but
-   *     the returned array will be the only reference to them
+   *     the returned array will be the only reference to them. Also, this won't clear the child
+   *     buffers.
    * @return The underlying {@link ArrowBuf buffers} that is used by this vector instance.
    */
   @Override
@@ -561,7 +562,7 @@ public ArrowBuf[] getBuffers(boolean clear) {
       list.add(validityBuffer);
       list.add(offsetBuffer);
       list.add(sizeBuffer);
-      list.addAll(Arrays.asList(vector.getBuffers(clear)));
+      list.addAll(Arrays.asList(vector.getBuffers(false)));
       buffers = list.toArray(new ArrowBuf[list.size()]);
     }
     if (clear) {

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

@@ -726,12 +726,13 @@ public void reset() {
 
   /**
    * Return the underlying buffers associated with this vector. Note that this doesn't impact the
-   * reference counts for this buffer so it only should be used for in-context access. Also note
-   * that this buffer changes regularly thus external classes shouldn't hold a reference to it
+   * reference counts for this buffer, so it only should be used for in-context access. Also note
+   * that this buffer changes regularly, thus external classes shouldn't hold a reference to it
    * (unless they change it).
    *
-   * @param clear Whether to clear vector before returning; the buffers will still be refcounted but
-   *     the returned array will be the only reference to them
+   * @param clear Whether to clear vector before returning, the buffers will still be refcounted but
+   *     the returned array will be the only reference to them. Also, this won't clear the child
+   *     buffers.
    * @return The underlying {@link ArrowBuf buffers} that is used by this vector instance.
    */
   @Override

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

@@ -704,7 +704,8 @@ public void reset() {
    * (unless they change it).
    *
    * @param clear Whether to clear vector before returning, the buffers will still be refcounted but
-   *     the returned array will be the only reference to them
+   *     the returned array will be the only reference to them. Also, this won't clear the child
+   *     buffers.
    * @return The underlying {@link ArrowBuf buffers} that is used by this vector instance.
    */
   @Override

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

@@ -396,12 +396,13 @@ public int getValueCapacity() {
 
   /**
    * Return the underlying buffers associated with this vector. Note that this doesn't impact the
-   * reference counts for this buffer so it only should be used for in-context access. Also note
-   * that this buffer changes regularly thus external classes shouldn't hold a reference to it
+   * reference counts for this buffer, so it only should be used for in-context access. Also note
+   * that this buffer changes regularly, thus external classes shouldn't hold a reference to it
    * (unless they change it).
    *
-   * @param clear Whether to clear vector before returning; the buffers will still be refcounted but
-   *     the returned array will be the only reference to them
+   * @param clear Whether to clear vector before returning, the buffers will still be refcounted but
+   *     the returned array will be the only reference to them. Also, this won't clear the child
+   *     buffers.
    * @return The underlying {@link ArrowBuf buffers} that is used by this vector instance.
    */
   @Override

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

@@ -25,6 +25,7 @@
 import org.apache.arrow.memory.RootAllocator;
 import org.apache.arrow.vector.complex.FixedSizeListVector;
 import org.apache.arrow.vector.complex.ListVector;
+import org.apache.arrow.vector.complex.ListViewVector;
 import org.apache.arrow.vector.complex.NonNullableStructVector;
 import org.apache.arrow.vector.complex.StructVector;
 import org.apache.arrow.vector.complex.UnionVector;
@@ -122,7 +123,10 @@ public void testListTypeReset() {
                 "VarList", allocator, FieldType.nullable(MinorType.INT.getType()), null);
         final FixedSizeListVector fixedList =
             new FixedSizeListVector(
-                "FixedList", allocator, FieldType.nullable(new FixedSizeList(2)), null)) {
+                "FixedList", allocator, FieldType.nullable(new FixedSizeList(2)), null);
+        final ListViewVector variableViewList =
+            new ListViewVector(
+                "VarListView", allocator, FieldType.nullable(MinorType.INT.getType()), null)) {
       // ListVector
       variableList.allocateNewSafe();
       variableList.startNewValue(0);
@@ -136,6 +140,13 @@ public void testListTypeReset() {
       fixedList.setNull(0);
       fixedList.setValueCount(1);
       resetVectorAndVerify(fixedList, fixedList.getBuffers(false));
+
+      // ListViewVector
+      variableViewList.allocateNewSafe();
+      variableViewList.startNewValue(0);
+      variableViewList.endValue(0, 0);
+      variableViewList.setValueCount(1);
+      resetVectorAndVerify(variableViewList, variableViewList.getBuffers(false));
     }
   }