Generating equals / hashcode / toString using annotation

Posted by Bruno Bieth on Stack Overflow See other posts from Stack Overflow or by Bruno Bieth
Published on 2010-03-29T03:09:39Z Indexed on 2010/03/29 3:13 UTC
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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

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