Are you required to define a Long variable as
Long myUserId = 1L; ?
How come you can't just do Long myUserId = 1; ?
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Paul Bellora
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Ben
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4Well you answered your first question yourself. – Dominic K Dec 05 '11 at 04:29
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I would guess that you could assign "1" (or any "int" valued compile time expression) and the compiler would do a cast to do the assignment. – Ira Baxter Dec 05 '11 at 04:31
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@IraBaxter: It will do a widening cast (for int to long), but not an autoboxing after that. – Thilo Dec 05 '11 at 04:33
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Checkout the following http://stackoverflow.com/questions/769963/javas-l-number-long-specification-question.. It has the explaination. – Josnidhin Dec 05 '11 at 04:34
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@Thilo: I missed the "Long" vs. "long". – Ira Baxter Dec 05 '11 at 04:36
2 Answers
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Long myUserId = 1; // error
does not work, because 1 is an int.
It will get auto-boxed to:
Integer myUserId = 1; // ok
It will also get widened to:
long myUserId = 1; // also ok
but not both.
So, yes, you have to say
Long myUserId = 1L;
which is a long that can get autoboxed into a Long.
As to why it works that way (or rather does not work in this case): Most likely because auto-boxing was added later (in Java5), and had to be absolutely backwards-compatible. That limited how "smooth" they could make it.
Thilo
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Because otherwise, Java defaults all numeric types to an Integer.
The only reason "1L" is even allowed to be assigned to a Long (instead of the primitive long) is due to the "auto-boxing" introduced with Java 5.
Without the "1L", behind-the-scenes, this looks like the following without the "L":
Long myUserId = Integer.valueOf(1);
... which I hope obviously explains itself. :-)
ziesemer
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