[GitHub] [arrow] lidavidm commented on a diff in pull request #34424: GH-15187: [Java] Made `reader` initialization lazy and added new `getTransferPair()` function that takes in a `Field` type

["lidavidm (via GitHub)" <gi...@apache.org>]

lidavidm commented on code in PR #34424:
URL: https://github.com/apache/arrow/pull/34424#discussion_r1228033482


##########
java/vector/src/main/java/org/apache/arrow/vector/BaseValueVector.java:
##########
@@ -143,6 +147,43 @@ long computeCombinedBufferSize(int valueCount, int typeWidth) {
     return allocator.getRoundingPolicy().getRoundedSize(bufferSize);
   }
 
+  /**
+   * Each vector has a different reader that implements the FieldReader interface. Overridden methods must make
+   * sure to return the correct type of the reader implementation to instantiate the reader properly.
+   *
+   * @return Returns the implementation class type of the vector's reader.
+   */
+  protected abstract Class<? extends FieldReader> getReaderImplClass();
+
+  /**
+   * Default implementation to create a reader for the vector. Depends on the individual vector
+   * class' implementation of `getReaderImpl()` to initialize the reader appropriately.
+   *
+   * @return Concrete instance of FieldReader by using lazy initialization.
+   */
+  public FieldReader getReader() {
+    FieldReader reader = fieldReader;
+
+    if (reader != null) {
+      return reader;
+    }
+    synchronized (this) {
+      if (fieldReader == null) {
+        try {
+          fieldReader =
+              (FieldReader) Class.forName(getReaderImplClass().getName()).getConstructor(getClass())

Review Comment:
   getReaderImplClass already returns a Class, why do we have to look it up again?



##########
java/vector/src/main/java/org/apache/arrow/vector/BaseValueVector.java:
##########
@@ -143,6 +147,43 @@ long computeCombinedBufferSize(int valueCount, int typeWidth) {
     return allocator.getRoundingPolicy().getRoundedSize(bufferSize);
   }
 
+  /**
+   * Each vector has a different reader that implements the FieldReader interface. Overridden methods must make
+   * sure to return the correct type of the reader implementation to instantiate the reader properly.
+   *
+   * @return Returns the implementation class type of the vector's reader.
+   */
+  protected abstract Class<? extends FieldReader> getReaderImplClass();
+
+  /**
+   * Default implementation to create a reader for the vector. Depends on the individual vector
+   * class' implementation of `getReaderImpl()` to initialize the reader appropriately.

Review Comment:
   Should be `{@link #getReaderImplClass}`? JavaDoc does not use Markdown.



##########
java/vector/src/main/java/org/apache/arrow/vector/BaseValueVector.java:
##########
@@ -143,6 +147,43 @@ long computeCombinedBufferSize(int valueCount, int typeWidth) {
     return allocator.getRoundingPolicy().getRoundedSize(bufferSize);
   }
 
+  /**
+   * Each vector has a different reader that implements the FieldReader interface. Overridden methods must make
+   * sure to return the correct type of the reader implementation to instantiate the reader properly.
+   *
+   * @return Returns the implementation class type of the vector's reader.
+   */
+  protected abstract Class<? extends FieldReader> getReaderImplClass();
+
+  /**
+   * Default implementation to create a reader for the vector. Depends on the individual vector
+   * class' implementation of `getReaderImpl()` to initialize the reader appropriately.
+   *
+   * @return Concrete instance of FieldReader by using lazy initialization.
+   */
+  public FieldReader getReader() {
+    FieldReader reader = fieldReader;
+
+    if (reader != null) {
+      return reader;
+    }
+    synchronized (this) {
+      if (fieldReader == null) {
+        try {
+          fieldReader =
+              (FieldReader) Class.forName(getReaderImplClass().getName()).getConstructor(getClass())

Review Comment:
   Also: why can't getReaderImplClass return a factory function instead of a class?



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