Java Tutorial · Java Basics · Lesson 11 of 37

Java Math

Math methods, rounding, random numbers and BigDecimal for money.

The Math class

Example 1

public class Main {
    public static void main(String[] args) {
        System.out.println(Math.max(5, 10) + " " + Math.min(5, 10));
        System.out.println(Math.abs(-7.5));
        System.out.println(Math.sqrt(64) + " " + Math.pow(2, 8));
        System.out.println(Math.round(2.5) + " " + Math.round(-2.5));
        System.out.println(Math.floor(2.7) + " " + Math.ceil(2.1));
        System.out.println(Math.floorMod(-7, 3) + " " + (-7 % 3));
    }
}

Output

Run this on your computer — see “Get Started” for setup.

Random numbers

Use ThreadLocalRandom or Random for random integers. For security tokens, use SecureRandom.

int dice = ThreadLocalRandom.current().nextInt(1, 7);  // 1..6

BigDecimal for money

double can't represent most decimals exactly. For money, use BigDecimal (or store cents in a long):

Example 2

import java.math.BigDecimal;
import java.math.RoundingMode;

public class Main {
    public static void main(String[] args) {
        System.out.println(0.1 + 0.2);
        BigDecimal a = new BigDecimal("0.10");
        BigDecimal b = new BigDecimal("0.20");
        System.out.println(a.add(b));
        BigDecimal price = new BigDecimal("19.99");
        BigDecimal total = price.multiply(BigDecimal.valueOf(3)).setScale(2, RoundingMode.HALF_UP);
        System.out.println(total);
    }
}

Output

0.30000000000000004
0.30
59.97

Run this on your computer — see “Get Started” for setup.

Test yourself

Which class should you use for exact decimal money calculations?

double
float
BigDecimal
Math

Show answer

Answer: BigDecimal