Operators

We already saw +, -, *, and / in earlier lessons. Java has a few more useful operators that we’ll meet now

public class Main {
    public static void main(String[] args) {
        int a = 17;
        int b = 5;

        System.out.println(a + b);   // addition
        System.out.println(a - b);   // subtraction
        System.out.println(a * b);   // multiplication
        System.out.println(a / b);   // division
        System.out.println(a % b);   // remainder (modulo)
    }
}

Output

The interesting one is a / b = 3, not 3.4. Why? Because a and b are both int. Java does integer division when both operands are integers: it throws away the decimal part. We saw this in an earlier lesson

If we want the decimal result, we need at least one double

public class Main {
    public static void main(String[] args) {
        double a = 17;
        int b = 5;
        System.out.println(a / b);   // 3.4
    }
}

The new operator is %, called modulo (or "remainder"). It gives the remainder of the division

public class Main {
    public static void main(String[] args) {
        System.out.println(17 % 5);   // 2
        System.out.println(20 % 4);   // 0
    }
}

17 / 5 = 3 with remainder 2, so 17 % 5 = 2. 20 / 4 = 5 exactly, so the remainder is 0

% is incredibly useful. The classic example: checking if a number is even

public class Main {
    public static void main(String[] args) {
        int n = 10;
        if (n % 2 == 0) {
            System.out.println("even");
        } else {
            System.out.println("odd");
        }
    }
}

Java has handy shortcuts

a++ is the same as a = a + 1
a-- is the same as a = a - 1
a += 5 is the same as a = a + 5
a -= 3 is the same as a = a - 3
a *= 2 is the same as a = a * 2
a /= 4 is the same as a = a / 4

You’ll see i++ in for loops literally everywhere

What about powers? Java doesn’t have a dedicated power operator. Instead, we use Math.pow

public class Main {
    public static void main(String[] args) {
        System.out.println(Math.pow(2, 3));   // 8.0
    }
}

Output is 8.0 (a double). Math.pow always returns a double, so even 2 to the power of 3 comes out as 8.0, not 8

The order of operations is the same as in math. Multiplication and division before addition and subtraction

public class Main {
    public static void main(String[] args) {
        System.out.println(2 + 3 * 4);     // 14, not 20
        System.out.println((2 + 3) * 4);   // 20
    }
}

When in doubt, add parentheses. They make the code easier to read anyway

Mission: Engine Diagnostics

The station's diagnostic console needs a quick arithmetic readout of two sensor values.

Create two int variables named a and b (any values you like). Then print, each on its own line, the result of: addition, subtraction, multiplication, integer division, and remainder.

Example

If the two numbers are 17 and 5, your program should print