Numbers and Math

Java can do arithmetic just like a calculator, and it uses many of the same symbols you already know from math class.

The basic math operators

• + for addition
• - for subtraction
• * for multiplication
• / for division
• % for remainder, also called modulo

int sum = 4 + 3;
int difference = 10 - 6;
int product = 5 * 2;
int quotient = 20 / 4;
int remainder = 7 % 2;

That last one, remainder, is worth a closer look. 7 % 2 equals 1, because 2 goes into 7 three times with 1 left over. This little operator turns out to be very useful, for example to check whether a number is even or odd.

A small trap with whole numbers

When you divide two int values, Java performs whole number division and drops anything after the decimal point. So 7 / 2 results in 3, not 3.5. If you want the decimal answer, at least one of the numbers involved needs to be a double.

double result = 7.0 / 2;
System.out.println(result);

That code would print 3.5 because 7.0 is treated as a decimal number from the start.

Updating a number quickly

It is extremely common to add one to a variable, so Java gives you a shortcut called the increment operator:

int points = 5;
points++;
System.out.println(points);

That would print 6. There is also a decrement operator, --, which subtracts one instead.

Numbers and math are everywhere in real programs, from calculating a shopping total to working out how many days are left until an event, so this is a skill you will lean on constantly.