real education

The arithmetic operators +, –, *, / are used in Java for addition, subtraction, multiplication, and division. The / operator denotes integer division if both arguments are integers, and floating-point division otherwise.
Integer remainder (that is, the mod function) is denoted by %. For example, 17/2 is 8, 17%2 is 1, and 17.0/2 is 8.5.

Example:
int n = 5;
int a = 2 * n; // a is 10

In java x += 4; is equivalent to x = x + 4;