Integer Division and Modulus

Division in Apex has a surprise for beginners: when both numbers are Integers, the result is also an Integer. The decimal part is cut off, not rounded.

Integer result = 7 / 2;
System.debug(result); // 3, not 3.5

Keeping the Decimal Part

If you need the fraction, make at least one side of the division a Decimal. You can use a Decimal literal or cast one of the values:

Decimal exact = 7.0 / 2; // 3.5
Decimal alsoExact = (Decimal) 7 / 2; // 3.5

Finding the Remainder with Math.mod

Many languages use the % operator to get the remainder of a division. Apex does not have a % operator. Instead, you call the Math.mod method:

Integer remainder = Math.mod(10, 3); // 1, because 10 = 3 * 3 + 1
Integer evenSplit = Math.mod(20, 5); // 0, because 20 divides evenly by 5

Where the Remainder Shows Up

The remainder is handy in many everyday coding tasks:

• Even or odd: Math.mod(n, 2) is 0 for even numbers and 1 for odd positive numbers
• Wrapping around: Math.mod(hour + 5, 24) wraps a clock time past midnight
• Splitting into groups: Math.mod(index, groupSize) gives the position of an item within its group

Whenever a problem repeats in cycles, think of Math.mod.