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map question from practice exam

Rachel Glenn
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Joined: Oct 24, 2012
Posts: 95
Here is the sample code:



I understand that the call to m2.get("a") returns NULL and the call to m2.get(2) returns "b".

I am surprised it is even allowed to compile. The answer says a warning is generated, but I guess the compiler sees that since a raw map is being passed in, that all type info is lost in the actual mangle function?
Greg Charles
Sheriff

Joined: Oct 01, 2001
Posts: 2853
    
  11

I see obvious compile errors at lines 5,6, and 11. Line 11 is an obvious typo, but I'm less sure what you're going for on lines 5 and 6.

The thing to remember about generics is they are a compile time concept. If you use a raw type, the compiler will warn you, but won't error out. The runtime won't even care ... at least, not until you try to use an object as a type it's not.
Rachel Glenn
Ranch Hand

Joined: Oct 24, 2012
Posts: 95
Greg Charles wrote:I see obvious compile errors at lines 5,6, and 11. Line 11 is an obvious typo, but I'm less sure what you're going for on lines 5 and 6.

The thing to remember about generics is they are a compile time concept. If you use a raw type, the compiler will warn you, but won't error out. The runtime won't even care ... at least, not until you try to use an object as a type it's not.


yes I do have some typos...but I see what you are saying. Your response made things clear for me in that if we do use the typed collections (as in Map<T>), the compiler will do type checking for us and issue errors if needed. But if we do NOT use the typed collections, but rather untyped version, like a plain old Map, then the most the compiler can do is issue warnings.
Himai Minh
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Joined: Jul 29, 2012
Posts: 773
Let me type up the code :

 
I agree. Here's the link: http://aspose.com/file-tools
 
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