Map.entry和entrySet（）泛型类型出错

Question

Here is the gone-wrone code

Set<Map.Entry> entrySet = new HashMap<Object,Object>().entrySet();

it comes up with a compile error

cannot convert from Set<Map.Entry<Object,Object>> to Set<Map.Entry>

But there should be just a warning from not using generic type in the case Map.Entry from Map.Entry<Object,Object>
But why here come out a compile error?
then I've suspected that the whole Set<Map.Entry> may be the reason,that is maybe Set<Map.Entry> ≠ set<Map.Entry<Object,Object>
but since Map.Entry ≈ Map.Entry<Object,Object>
why not Set<Map.Entry> ≈ set<Map.Entry<Object,Object>

I've find the relavent questions,but my question is this case is something different.
To be more spacific,why when I use Set<Map.Entry> ,I can't event get through compile and get an error but not just a warning?
But in another case,for example ArrayList li = new ArrayList<String>();
I can get through compile and just get a warning "ArrayList is a raw type. References to generic type ArrayList should be parameterized"

Answer 1

It's because of the set<> generic type.For example,
HashSet<String> s1 = new HashSet<Integer> may goes wrong.
If the right side is a Integer generic type instance,then the reference variable's generic type in the left side cannot be String.
so String ≠ Integer like Map.Entry ≠ Map.Entry<Object,Object>