Public Object: Don't create multiple annotations with the same simple name

Don't create multiple annotations with the same simple name

Nobody reads imports. Good IDEs do their best to pretend imports don't even exist - they'll hide 'em from you, and manage them for you. They'll even add imports on demand when you're writing new code.

Suppose you create your own, say @Inject or @RequestScoped annotation. In the code, it's practically impossible to differentiate between this and a Guice-supplied annotation:

package com.publicobject.pizza;

import com.google.common.base.Preconditions;
import com.google.common.collect.ImmutableSet;
import com.google.inject.Injector;
import com.google.inject.Provider;
import com.publicobject.pizza.annotation.RequestScoped;
import com.publicobject.pizza.annotation.Inject;
import com.publicobject.pizza.geography.GeographyService;
import com.publicobject.pizza.hr.EmployeeRoster;

@RequestScoped
public class PizzaStore {
  @Inject PizzaStore(GeographyService geography,
      EmployeeRoster workers) { ... }
}

Your head will explode debugging problems if the wrong annotation is applied. Guice can detect some problems (blowing up on a mismatched scope annotation) but it's still risky business.

# posted by Jesse Wilson on Monday, July 21, 2008

Before writing tedious long annotation names like @PostConstructInterceptorInject usage of inner classes may another solution:

public class PostConstructInterceptor {
public static @interface Inject {}
}

So you can decide to import the annotation directly or its outer class like

public class PizzaStore {
@PostConstructInterceptor.Inject
public PizzaStore(...) {}
}

# posted by tzwoenn on July 22, 2008 12:54 AM

This is one of the really irritating things about JPA and Hibernate Annotations -- e.g. the annotations javax.persistence.Entity and org.hibernate.annotations.Entity (which provides 'additional information' on top of what's in j.p.Entity). This kind of thing (there are a few examples) leads to confusion and a lot of forehead-slapping realizations after long debugging.

# posted by Cowan on July 23, 2008 7:30 PM