My workspace is configured to mark a "Missing @Override annotation" with a Warning, even for interface methods.

Consider this interface:

package test;
public interface I {
	void myMethod(String a, int b);
}

and this Groovy class:

package test
class A implements I {
	public void myMethod(String a, int b) {
		def i = new I() {
			public void myMethod(String a1, int b1) {
			}
		}
	}
}

You can see that A.myMethod(String, int) declaration is not marked with a warning, while new I().myMethod(String, int) is.