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Because the constants on the right-hand-sides of these assignments are integers, not longs, the multiplication is done with integers, and the final int result is then converted to a long. "a" is less than the maximum value of an int by about a factor of 25, but "b" is way over, so "b" overflows and you end up with an unexpected value -- i.e., you get (int) (24*60*60*1000*1000L), which, just by happenstance, is about 5 times as large as "a", rather than 1000 times.

If you change the declaration of "b" to be

public static final long b =24*60*60*1000*1000L;

(note that "L" on the end) then the multiplies are done using longs, and you'll get the answer you expect.

Yep. We discuss this one in detail in Puzzle 3 ("Long Division"). Note that a better fix is:

By making the first factor in the sequence of multiplications a long, we don't have to worry about where the overflow occurs: the entire computation is done using longs.

Regards,

Josh and Neal

Originally posted by Ernest Friedman-Hill: Because the constants on the right-hand-sides of these assignments are integers, not longs, the multiplication is done with integers, and the final int result is then converted to a long. "a" is less than the maximum value of an int by about a factor of 25, but "b" is way over, so "b" overflows and you end up with an unexpected value -- i.e., you get (int) (24*60*60*1000*1000L), which, just by happenstance, is about 5 times as large as "a", rather than 1000 times.

If you change the declaration of "b" to be

public static final long b =24*60*60*1000*1000L;

(note that "L" on the end) then the multiplies are done using longs, and you'll get the answer you expect.

Joshua Bloch <br />Author of <a href="http://www.amazon.com/exec/obidos/ASIN/0201310058/ref=ase_electricporkchop" target="_blank" rel="nofollow">Effective Java</a> and coauthor of <a href="http://www.amazon.com/exec/obidos/ASIN/032133678X/ref=ase_electricporkchop" target="_blank" rel="nofollow">Java Puzzlers</a>

Ramaswamy Srinivasan
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Joined: Aug 31, 2004
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Hi Ernets, Josh and Neal

Thanks a lot for the explanation. This is making things lucid.