Advanced Puzzlers - Java Puzzlers: Traps, Pitfalls, and Corner Cases - page 267

resulting in false positives. This can be accomplished, for example, by choosing large but distinct
long values for x and z , and a double value that is close to both long values for y . The following
program does exactly that. It prints TRue true false , clearly demonstrating the nontransitivity of
the == operator over primitives:
public class Transitive {
public static void main(String[] args) throws Exception {
long x = Long.MAX_VALUE;
double y = (double) Long.MAX_VALUE;
long z = Long.MAX_VALUE - 1;
System.out.print ((x == y) + " "); // Imprecise!
System.out.print ((y == z) + " "); // Imprecise!
System.out.println(x == z); // Precise
}
}
The lesson is: Beware of lossy widening primitive conversions to float and double. They are
silent but deadly. They can violate your intuition and cause subtle bugs ( Puzzle 34 ). More generally,
beware of mixed-type operations ( Puzzles 5 , 8 , 24 , and 31 ). The lesson for language designers is the
same as for Puzzle 34 : Silent loss of precision confuses programmers.
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