Math, Wrapper Classes, Casting and Overflow

Math, wrapper classes, casting, and the edge of int

Math is a class of static methods, so you call them on the class name. The four in the AP subset are Math.abs, Math.pow, Math.sqrt and Math.random. Math.pow and Math.sqrt always return a double, even for Math.pow(2, 3), which prints as 8.0.

Math.random() returns a double in the interval from 0 (included) to 1 (excluded). The pattern for a random integer from low to high inclusive is:

(int) (Math.random() * (high - low + 1)) + low

The + 1 is there because the count of integers from low to high inclusive is high - low + 1.

Casting with (int) truncates toward zero; it does not round. It also binds tightly, so (int) 7.9 / 2 is 7 / 2 = 3, while (int) (7.9 / 2) is (int) 3.95 = 3 as well but for a different reason — change the numbers and the two differ. Integer division discards the remainder, so 1 / 2 * 3.0 is 0.0.

Wrapper classes Integer and Double let a primitive be treated as an object, and they carry the constants Integer.MAX_VALUE and Integer.MIN_VALUE. Arithmetic that passes those limits does not throw an exception: it wraps around silently.