Ternary Operator

At a cinema ticket counter: "Under 12? Child ticket. Otherwise, adult ticket." That's one question and two possible answers. Java has an operator built for exactly this: the ternary operator, condition ? valueIfTrue : valueIfFalse. It's called ternary because it takes three parts, and it lets you pick between two values in a single expression.

How It Works

public class Ticket {
    public static void main(String[] args) {
        int age = 9;
        String type = age < 12 ? "Child" : "Adult";
        int price = age < 12 ? 120 : 250;
        System.out.println(type + " ticket: Rs. " + price);
    }
}

Child ticket: Rs. 120

How it works

1. Line 4 checks age < 12. It's true for 9, so the whole expression becomes "Child", the value after ?.
2. Line 5 asks the same question and picks 120.
3. If age were 30, the values after : would be chosen: "Adult" and 250.

Try it yourself: change age to 12. Which ticket do you get, and why?

Ternary vs if-else

The ternary on line 4 does the same job as this if-else:

String type;
if (age < 12) {
    type = "Child";
} else {
    type = "Adult";
}

You'll learn if-else properly in "Java If-Else Statements".

Result Type

Both sides of a ternary should have the same type, or types Java can combine. When they're different numeric types, the usual promotion rules apply:

public class Mixed {
    public static void main(String[] args) {
        boolean member = true;
        double discount = member ? 10 : 2.5;
        System.out.println("Discount: " + discount + "%");
    }
}

Discount: 10.0%

The two possible values are 10 (an int) and 2.5 (a double), so the result is a double, and 10 prints as 10.0.

Common Mistakes

Using a ternary for actions. age < 12 ? System.out.println("Child") : System.out.println("Adult"); doesn't compile, because println returns nothing. Use if-else for actions.

Forgetting that only one side runs. Only the chosen value is evaluated, so a method call on the other side never happens. That's usually what you want, but it surprises people while debugging.

Getting the order wrong. It's always condition ? ifTrue : ifFalse. A quick check: the true value sits next to the question mark.

Practice

1. Easy: Use a ternary to print "Pass" when marks are 35 or more, and "Fail" otherwise.
2. Harder: Use a ternary to set the delivery charge to 0 when the order total is Rs. 499 or more, and Rs. 40 otherwise. Print the final amount for totals of 450 and 520.

Key Takeaways