Java: Automatic equals() and hashCode()

Question

Implementing equals() and hashCode() for simple data POJOs is cluttering my code and maintaining is tedious.

What are the libraries handling this automatically?
I prefer bytecode instrumentation over AOP approach due to performance reasons.

Update: Topic of necessity of implementing equals() and hashCode() has been discussed, here's my point:

Isn't it better to have it done right upfront with minimal effort rather than digging in the code, adding hC/eq when it comes to it?

Answer 1

Project Lombok provides the annotation @EqualsAndHashCode which will generate equals() and hashCode() for your Java classes. Of course there are some drawbacks in comparison to manually implementing these methods, so make sure you read the "small print" on the linked page.

Answer 2

Java 7 & later

While not the panacea you requested, writing the hashCode override is a bit easier now as of Java 7 and later.

Objects.hashCode & Objects.hash

As of Java 7, the Objects class offers a couple of utility methods for generating hash code values.

See my Answer on a related Question for more discussion.

• If your hashCode (and equals) override is based on a single member of your class, use Objects.hashCode( member ).
• If your hashCode (and equals) override is based on multiple attribute of your class, use Objects.hash( memberA , memberB , memberC ).

Single member, not tolerating a NULL

@Override
public int hashCode() {
    return this.member.hashCode() ;  // Throws NullPointerException if member variable is null.
}

Single member, tolerating a NULL

@Override
public int hashCode() {
    return Objects.hashCode( this.member ) ;  // Returns zero (0) if `this.member` is NULL, rather than throwing exception.
}

Multi-member

@Override
public int hashCode() {
    return Objects.hash( this.memberA , this.memberB , this.memberC  ) ;  // Hashes the result of all the passed objects’ individual hash codes.  
}