CODEWITHSUNDEEP
javaannotations
WinOrWin
WinOrWin

Reputation: 2117

Annotation concepts in Java

To quote this link :

Some developers think that the Java compiler understands the tag and work accordingly. This is not right. The tags actually have no meaning to the Java compiler or runtime itself. There are tools that can interpret these tags

.

If the information contained in the annotation is only metadata, why wont my code compile if I annotate wrongly ? That particular annotation should be simply ignored right ?

Edit :

Just to provide an example... A simple JAX-RS web service on Jersey uses an annotation like :

@Path("mypath")

Now, if I change this to :

@Paths("mypath")

OR

@Path(123)

it should NOT stop me from compiling the code according to the above link...

Upvotes: 0

Views: 316

Answers (2)

TMN
TMN

Reputation: 3070

Annotations are basically a special form of interface, so the compiler has to be able to load the annotation definition in order to encode the information so it can be included in the class file. Once it's in the class file, the class loader will load it as part of the class, so that annotation-processing tools can access the information. The compiler will verify that only defined arguments are used, as well as supplying default values for attributes that aren't specified (and have defaults defined).

Upvotes: 0

Jon Skeet
Jon Skeet

Reputation: 1499770

The article is wrong for at least some annotations. Thinks like @SuppressWarnings and @Override the compiler does have very specific knowledge. In fact, the article points this out itself:

Metadata is used by the compiler to perform some basic compile-time checking. For example there is a override annotation that lets you specify that a method overrides another method from a superclass.

Quite how it can be used by the compiler if "the tags actually have no meaning to the Java compiler", I don't know...

Additionally, even for annotations that the compiler doesn't attach any semantic meaning to, it will still verify that when you try to specify particular arguments etc, that those arguments have sensible names and types for the annotation you're using.

Upvotes: 5

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