why we could create instance of bitmap

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C#2.0

C#

Bitmap is a seald class.why i can create instance.????while with The graphics are not??

Posted 11-Feb-11 22:32pm

User 7427435

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3 solutions

Solution 3

Sealed does not mean you cannot use it: it means that you cannot inherit from it.

You can create an instance of any class that is not marked static: Since C# has no concept of global variables, a class that you could not instantiate would not be usable.

Why is Bitmap a sealed class? Probably to stop people adding to it and expecting the additions to work in the bitmap file. Given that the format of a Bitmap file is fixed, that would make sense.

The Graphics object on the other hand is not sealed: you can inherit from it and enhance it. That at least allows for facilities to be added if the required draw method does not exist.

Posted 11-Feb-11 22:52pm

OriginalGriff

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Sergey Alexandrovich Kryukov 13-Feb-11 0:49am

Best answer so far, enough detail, my 5, proposed as a final answer.
--SA

Solution 2

A sealed class cannot be inherited and it cannot be abstract.
So it definitely possible create a new instance.

Cheers

Posted 11-Feb-11 22:47pm

Estys

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Sergey Alexandrovich Kryukov 13-Feb-11 0:47am

Correct, my 4. Griff also added some rationale about Graphics and Bitmap, which is required by the question.
--SA

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Toli Cuturicu · Accepted Answer · 2011-02-11T22:43:00

Solution 1

Read some documentation.
sealed = cannot inherit from that class; can instantiate it, of course if it has a public constructor.
Graphics class does not have a public constructor. That's why you can't instantiate it that way. You can however create an instance of it through other means (static methods, e.Graphics from events...)

Posted 11-Feb-11 22:43pm

Toli Cuturicu

Updated 11-Feb-11 22:45pm

v2

Comments

Estys 12-Feb-11 4:50am

a much better answer then mine.

Sergey Alexandrovich Kryukov 13-Feb-11 0:46am

Correct explanation in principle, but the question is also about Bitmap, not only Graphics.
--SA