Double brace initialisation (anonymous inner class) with diamond operator

Question

I am wondering why the second map declaration (using the diamond operator) does not compile when the first one does. Compilation error:

error: cannot

Answer 1

Note that you could also omit the diamond altogether. However, while this compiles, it's only because it's ignoring the Java generics and leans on the fact that Java is backwards compatible with previous versions.

Map map1 = new HashMap() { //compiles fine
    {
        put("abc", "abc");
    }
};