What is Annotation interface

[jacob deiter]

Can you please explain what is this interface "Annotation"?

Annotation

To create a custom annotation, the following syntax should be used

public @interface Test {
}

then what are the difference between Annotation Interface and "@interface"?

[Campbell Ritchie]

Did you read the documentation for that interface? Have you looked at the Jva® Languge Specification (=JLS) section mentioned there?

[Stephan van Hulst]

Java is a reflective language, meaning you can use some language features in code as if they're objects. An example of this is the Class class. Annotation is similar. All types that are declared using @interface will automatically also implement the Annotation interface. This interface is used in reflective code (such as annotation processors) to inspect code that was annotated some way.

For instance, if you have a class that contains a declaration like this:

@Test(expected = SomeException.class)
void testThatSomeMethodThrowsSomeException() {
  //
}

You can write an annotation processor that looks like this:

for (Class<?> testClass: testClasses) {
  for (Method method: testClass.getMethods()) {
    Test annotation = method.getAnnotation(Test.class);
    if (annotation == null)
      continue;

    Class<? extends Throwable> expectedExceptionType = annotation.expected;

    // etc. etc.
  }
}