zhztheplayer commented on a change in pull request #10652:
URL: https://github.com/apache/arrow/pull/10652#discussion_r716209350
##########
File path:
java/dataset/src/main/java/org/apache/arrow/dataset/scanner/ScanOptions.java
##########
@@ -26,12 +26,16 @@
/**
* Constructor.
- * @param columns Projected columns. Empty for scanning all columns.
* @param batchSize Maximum row number of each returned {@link
org.apache.arrow.vector.ipc.message.ArrowRecordBatch}
+ * @param columns Projected columns. Null for scanning all columns.
*/
- public ScanOptions(String[] columns, long batchSize) {
- this.columns = columns;
+ public ScanOptions(long batchSize, String[] columns) {
Review comment:
Just to clarify, would you suggest to change the constructor to
something like:
```Java
public ScanOptions(long batchSize, Optional<String[]> columns)
```
or
```Java
public ScanOptions(Optional<String[]> columns, long batchSize)
```
? The issue we are trying to solve here is to make empty `columns` select
zero columns rather than all columns (previous behavior). I don't think we can
do anything to keep the compatibility when empty `columns` is specified.
Or by backwards compatibility you meant the compatibility in future changes?
Then I don't have strong preference on using Optionals or nulls. Or maybe
adding a builder pattern will also help? We will certainly have more options in
future.
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