Should You Use Objects.hash() or Implement Your Own hashCode()?

What are the advantages and disadvantages of using Objects.hash() compared to implementing a custom hashCode() method in Java?

When developing in Java, defining an efficient hashCode() method is crucial for performance, particularly when using collections like HashMap or HashSet. Two common approaches to implementing hashCode() are utilizing the utility method Objects.hash() and writing a custom hashCode() method. Both approaches have distinct advantages and disadvantages that can influence your choice depending on the use case.

// Implementation using Objects.hash()
@Override
public int hashCode() {
    return Objects.hash(id, timestamp, severity, thread, classPath, message);
}

// Custom implementation
@Override
public int hashCode() {
    int hash = 5;
    hash = 67 * hash + (int)(this.id ^ (this.id >>> 32));
    hash = 67 * hash + (int)(this.timestamp ^ (this.timestamp >>> 32));
    // Add other fields similarly
    return hash;
}

Causes

• Performance Impact: Custom implementations can be optimized for specific classes, leading to better performance than the generic Objects.hash() method.
• Simplicity: Objects.hash() provides a simple and concise way to implement hashCode(), reducing boilerplate code.
• Readability: Custom implementations may be clearer for complex logic, while Objects.hash() benefits those looking for succinctness.

Solutions

• Use Objects.hash() for most cases where performance isn't a critical concern and simplicity is preferred.
• Implement a custom hashCode() when performance is paramount, for instance, in high-traffic applications or when special distribution properties of the hash values are required.
• Consider code maintainability and readability when implementing your choice.

Mistake: Overusing Objects.hash() without considering performance implications.

Solution: Profile your application to determine if performance is a concern, especially in applications with high-frequency hashCode() calls.

Mistake: Not considering hashCode() in relation to equals().

Solution: Ensure that whenever equals() is overridden, hashCode() is also overridden to maintain the contract between them.