content.md

Chain of boolean expressions

boolean isLeapYear(int year) {
    return year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);
}

The first boolean expression uses the remainder operator to check if the year is evenly divided by 4.

• If the year is not evenly divisible by 4, then the chain will "short circuit" due to the next operator being a logical AND (&&), and will return false.
• If the year is evenly divisible by 4, then the year is checked to not be evenly divisible by 100.
• If the year is not evenly divisible by 100, then the expression is true and the chain will "short-circuit" to return true, since the next operator is a logical OR (||).
• If the year is evenly divisible by 100, then the expression is false, and the returned value from the chain will be if the year is evenly divisible by 400.

year	year % 4 == 0	year % 100 != 0	year % 400 == 0	is leap year
2020	true	true	not evaluated	true
2019	false	not evaluated	not evaluated	false
2000	true	false	true	true
1900	true	false	false	false

The chain of boolean expressions is efficient, as it proceeds from testing the most likely to least likely conditions.