Generating equals / hashcode / toString using annotation

Question

I believe I read somewhere people generating equals / hashcode / toString methods during compile time (using APT) by identifying which fields should be part of the hash / equality test. I couldn't find anything like that on the web (I might have dreamed it ?) ...

That could be done like that :

public class Person {
  @Id @GeneratedValue private Integer id;

  @Identity private String firstName, lastName;
  @Identity private Date dateOfBirth;

  //...
}

For an entity (so we want to exlude some fields, like the id).

Or like a scala case class i.e a value object :

@ValueObject
public class Color {
  private int red, green, blue;
}

Not only the file becomes more readable and easier to write, but it also helps ensuring that all the attributes are part of the equals / hashcode (in case you add another attribute later on, without updating the methods accordingly).

I heard APT isn't very well supported in IDE but I wouldn't see that as a major issue. After all, tests are mainly run by continuous integration servers.

Any idea if this has been done already and if not why ? Thanks

Answer 1

I'm using Project Lombok for this.

Answer 2

While Pojomatic does not do compile-time bytecode manipulation, it does support easy creation of equals, hashCode and toString methods, using annotations to customize their behavior.

Answer 3

Google's solution in library AutoValue: https://github.com/google/auto/tree/master/value uses @AutoValue annotation + generation of sources before compilation.

Several competing solutions are discussed in the following presentation: https://docs.google.com/presentation/d/14u_h-lMn7f1rXE1nDiLX0azS3IkgjGl5uxp5jGJ75RE/edit