Java Math Class

The Math class (in java.lang, no import needed) has static methods for common maths. You call them like Math.sqrt(16).

Common methods

public class Main {
    public static void main(String[] args) {
        System.out.println(Math.max(10, 25));
        System.out.println(Math.min(10, 25));
        System.out.println(Math.abs(-7.5));
        System.out.println(Math.pow(2, 10));      // 2 to the power 10
        System.out.println(Math.sqrt(81));
        System.out.println(Math.cbrt(27));        // cube root
        System.out.println(Math.PI);
    }
}

Rounding

public class Round {
    public static void main(String[] args) {
        double x = 4.5;
        System.out.println(Math.round(x));    // 5   nearest whole number
        System.out.println(Math.round(4.4));  // 4
        System.out.println(Math.ceil(4.1));   // 5.0 always up
        System.out.println(Math.floor(4.9));  // 4.0 always down
        System.out.println(Math.round(-4.5)); // -4  (rounds half up)
        System.out.println(Math.rint(4.5));   // 4.0 (half to even)
    }
}

Method	What it does
round(x)	Nearest whole number (as long or int)
ceil(x)	Up to the next whole number (double)
floor(x)	Down to the whole number (double)

Random numbers

Math.random() gives a double from 0.0 up to (but not including) 1.0. To get a number in a range, use a formula or the Random class.

import java.util.Random;

public class Rand {
    public static void main(String[] args) {
        double r = Math.random();
        System.out.println(r >= 0.0 && r < 1.0);

        int dice = (int) (Math.random() * 6) + 1;        // 1 to 6
        System.out.println(dice >= 1 && dice <= 6);

        Random rnd = new Random(42);                      // a fixed seed gives the same numbers
        System.out.println(rnd.nextInt(100));
        System.out.println(rnd.nextInt(100));
        System.out.println(new Random().nextInt(1, 7) <= 6);   // 1 to 6, easy way
    }
}

With a fixed seed (42) the Random class always gives the same numbers, which is good for tests. Without a seed the numbers are different on every run.

Exact math

Normal int math can overflow without any error. The Math.xxxExact() methods throw an exception instead:

public class Exact {
    public static void main(String[] args) {
        int big = Integer.MAX_VALUE;
        System.out.println(big + 1);                 // wrong value, no error
        try {
            System.out.println(Math.addExact(big, 1));
        } catch (ArithmeticException e) {
            System.out.println("Caught: " + e.getMessage());
        }
    }
}

Division by zero

public class Zero {
    public static void main(String[] args) {
        System.out.println(5.0 / 0);        // Infinity: no error for decimals
        System.out.println(0.0 / 0);        // NaN: not a number
        System.out.println(5 / 0);          // int: exception
    }
}

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