Let's have a code block like the following one:

  final Callable<String> callable = new Callable<String>() {

            @Override
            public String call() throws Exception {
                return "test";
            }
        };

Hints suggest to use diamond inference, so above code would be changed to:

 final Callable<String> callable = new Callable<>() {

            @Override
            public String call() throws Exception {
                return "test";
            }
        };

But the lattest code will not compile, due to:

 error: cannot infer type arguments for Callable;
        final Callable<String> callable = new Callable<>() {
  reason: cannot use '<>' with anonymous inner classes