[REEF-1390] Make Optional's toString() and hashCode() computed on demand

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 0.15
• Component/s: REEF
• Labels: easyfix performance
• Assignee: Wonook
• Reporter: Woo-Yeon Lee
• Created: 15/May/16 01:53
• Updated: 17/May/16 15:31
• Resolved: 17/May/16 15:29

Description

Optional's constructor preloads valueStr and valueHash for its toString() and hashCode() methods respectively, even when those methods are never invoked during the life of the object.

  private Optional(final T value) {
    this.value = value;
    this.valueStr = "Optional:{" + value + "}";
    this.valueHash = value.hashCode();
  }

It incurs unnecessary overhead, and the problem becomes worse if the size of value is huge and T's hashcode() requires heavy computation.

They should be done in toString() and hashCode() methods on demand, respectively like below:

  private Optional(final T value) {
    this.value = value;
  }

  @Override
  public String toString() {
    return "Optional:{" + this.value + "}";
  }

  @Override
  public int hashCode() {
    return this.value.hashCode();
  }

+As a related issue, when value is null, it's better to return a reference of a static variable for empty Optional, not making separate objects every time. The following is the current code.

  public static <T> Optional<T> empty() {
    return new Optional<>();
  }