[ARROW-13847] Avoid unnecessary copies of collection

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 6.0.0
• Component/s: Java
• Labels: pull-request-available
• External issue URL: https://github.com/apache/arrow/issues/29468
• Assignee: Laurent Goujon
• Reporter: Laurent Goujon
• Created: 01/Sep/21 16:42
• Updated: 11/Jan/23 08:35
• Resolved: 26/Sep/21 03:15

Description

There are several occurences of unnecessary copies of collections in Arrow Java code.

One typical example is for a constructor to copy a collection provided as an argument, and then invoking Collections2 method to create a immutable copy of it, like for Schema (https://github.com/apache/arrow/blob/247a7a9bf1b7090b1bffc14bec84d188dccb52dc/java/vector/src/main/java/org/apache/arrow/vector/types/pojo/Schema.java#L113)

  /**
   * Constructor with metadata.
   */
  public Schema(Iterable<Field> fields,
                Map<String, String> metadata) {
    List<Field> fieldList = new ArrayList<>();
    for (Field field : fields) {
      fieldList.add(field);
    }
    this.fields = Collections2.immutableListCopy(fieldList);
    this.metadata = metadata == null ? Collections.emptyMap() : Collections2.immutableMapCopy(metadata);
  } 

Issue Links

• links to: GitHub Pull Request #11063