Java 8 implementation isLeapYear. What does boolean operator mean?
I am researching java 8 implementation of Date API and found this
Checks if the year is a leap year, according to the ISO proprietary calendar system rule.
This method applies the current rules for leap years throughout the chart. In general, a year is a leap year if it is divisible by four without a remainder. However, years divisible by 100 do not jump years, except for years divisible by 400.
For example, 1904 is a leap year when it is divisible by 4. 1900 was not a leap year because it is divisible by 100, however 2000 was a leap year because it is divisible by 400.
The calculation will fail - the application of the same rules in the distant future and the distant past. This is historically inaccurate, but true for the ISO-8601 standard.
public boolean isLeapYear(long prolepticYear) {
return ((prolepticYear & 3) == 0) && ((prolepticYear % 100) != 0 || (prolepticYear % 400) == 0);
}
But give us prolepticYear and 3.
11111001111 & 00000000011 00000000011
which means "proleptic" and 3.
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prolepticYear & 3
let it be a little different. 3
in binary format 11
. Thus, prolepticYear
and 11
will be equal to zero only when the last two bits of prolepticYear
are equal to zero. (which is actually called a bit mask).
Now think a little differently:
0100 - (4 in decimal, has last two bits zero)
1000 - (8 in decimal, has last two bits zero)
1100 - (12 in decimal, has last two bits zero)
... these are numbers divisible by four
Usually the operation &
is faster than %
.
Sometimes &
also used for other purposes (the %
operation can give negative numbers, &
it won't - how the bucket internally is selected HashMap
based on possible negative values Key#hashcode
, but not here)
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