Using the Math Class

Math's Static Methods

Math is a built-in class of static methods — no object, no new, just call it directly by its class name:

Math.abs(-4);     // 4 — absolute value
Math.pow(2, 3);   // 8.0 — 2 to the power of 3
Math.sqrt(9);     // 3.0
Math.random();    // a double >= 0.0 and < 1.0

These all return a value, so — same rule as the last lesson — you must actually use what they return.

Random Numbers in a Range

Math.random() alone gives a double in [0.0, 1.0) — including 0.0, never reaching 1.0. That's rarely useful on its own; you stretch and shift it to get the range you actually want:

int rnd = (int)(Math.random() * 10);      // an int from 0-9 (10 possible values)
int rnd2 = (int)(Math.random() * 10) + 1; // an int from 1-10 (shifted up by 1)

The general recipe: multiply by how many values you want, cast to int to drop the decimal, then add the minimum to shift the whole range up.

// A random autonomous delay between 1 and 4 seconds
double delay = Math.random() * 3.0 + 1.0; // [1.0, 4.0)

// A random starting position index, 0 through 2 (3 choices)
int startPos = (int)(Math.random() * 3);

The parentheses matter: (int)(Math.random() * 10) casts the whole scaled expression; (int)Math.random() * 10 casts Math.random() alone first — which truncates it to 0 every time, then multiplies by 10, always giving 0.

Common Pitfalls

Forgetting the parentheses around the scaled expression. (int)Math.random() * 10 always evaluates to 0 — the cast has to wrap the whole Math.random() * range expression.
Off-by-one on the range size. For an inclusive range like 1-10, the range size is 10, not 9 — count how many distinct values you actually want.
Ignoring the return value. Math.abs(x); on its own line compiles but does nothing useful — the result has to be stored or used.

Key Takeaways

Math methods are static — call them as Math.methodName(...), no object needed.
Math.random() returns a double in [0.0, 1.0) — 0.0 possible, 1.0 never reached.
To get a random int in a range: (int)(Math.random() * range) + min, where range is the count of possible values.
The parentheses around Math.random() * range are required — casting only Math.random() breaks the formula.

Derived from csawesome-2026: unit-1-using-objects-and-methods/1.11-using-the-math-class.md (CSA 1.11)