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Problem with this code

Niranjan Deshpande
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Joined: Oct 16, 2005
Posts: 1277
final int i = 100;
byte b = i;
System.out.println(b);

int i = 100;
byte b = i;
System.out.println(b);


The first code snippet compiles and gives output 100. Why does the 2nd code give compiler error??


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Jesus Angeles
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Joined: Feb 26, 2005
Posts: 2057
the first one:
the compiler is able to assign a value to b, as at compile time, the data is available (it is final, so the compiler knows it is the value and will never change).

the second one:
the value that will be assigned to b will be available only during runtime. but you cannot assign directly like that; as int is larger than byte.
Mihai Lihatchi
Ranch Hand

Joined: Oct 28, 2005
Posts: 138

It is weird indeed. This is connected to the compiler I believe.
If you change the first snippet of code to


final int i = 130;
byte b = i;
System.out.println(b);

the code generates the compilation error you would expect anyhow (because i>128).
My assumption is this:

The compiler checks whether a loss of precision MAY take a place but i is final AND already asigned to 100 (in bit domain) therefore the compiler knows it can fit into a byte and this cannot change and I believe that for optimization purposes does not generate the error.

However if i>127 the error is generated as the conversion MUST take place and there is a big chance for the precision to be lost.
However this trick is much too subtle.. I would have certainly overlooked it.
You have a very good question .. I had to copy the code into Eclipse and test it to be shore that it doesn't throw a compilation error.


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Barry Gaunt
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Joined: Aug 03, 2002
Posts: 7729
This question has been asked many times in this forum. Please search through past posts.


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Mihai Lihatchi
Ranch Hand

Joined: Oct 28, 2005
Posts: 138

Sorry .
I am new here . I rushed into posting.
A Kumar
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Joined: Jul 04, 2004
Posts: 979
Hi..

There are certain rules...that govern implicit casting...

Have a look at this post..

Implicit casting

If you search ...you cvan get still further posts that addresses

your doubt..

Let me know if you find it useful..

 
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