Ternary operator

In if-statements, we change the flow of control in programs. With ternary statements, we assign a variable based on a conditional expression.

A simpler purpose

While if-statements can become complex, ternary statements tend to be simpler. We use them to assign variables based on a logical expression.

Two examples

This program uses the ternary operator in two places. After the condition, we type the question mark, and then we separate the true and false conditions with a ":" char.

Note The two results in a ternary must have the same type. In the example 4 and 1 are both ints. A mismatch error will otherwise occur.

Detail In a ternary, this can be any expression that evaluates to true or false. Even a method may be called.

Result This is the value that was determined by the logical condition. We can return a ternary from a method.

public class Program {
    public static void main(String[] args) {

        int value1 = 100;

        // If value1 equals 100, set value2 to 4.
        // ... Otherwise set value2 to 1.
        int value2 = value1 == 100 ? 4 : 1;
        System.out.println(value2);

        // If value1 is greater than or equal to 200, set value3 to a string literal.
        // ... Otherwise, assign a different string literal.
        String value3 = value1 >= 200 ? "greater" : "lesser";
        System.out.println(value3);
    }
}4
lesser

Return

We can use a ternary expression in the result statement of a method. This sometimes gives us elegant code. It is also shorter to type.

Here The getStringMultiplier method returns 1000 if the argument string ends in K, and 1 otherwise.

public class Program {

    public static int getStringMultiplier(String test) {
        // Return 1000 if the string ends in K, and 1 if it does not.
        return test.endsWith("K") ? 1000 : 1;
    }

    public static void main(String[] args) {

        System.out.println(getStringMultiplier("125K"));
        System.out.println(getStringMultiplier("?"));
        System.out.println(getStringMultiplier("10K"));
    }
}1000
1
1000

Type mismatch

Both results of a ternary operation must be of the same type, or must be able to convert to that type. Here an error results because 0 is not a String.

public class Program {
    public static void main(String[] args) {

        int v = 1000;
        // Both possible results from a ternary must have valid types.
        String result = v == 1000 ? "one thousand" : 0;
    }
}
Exception in thread "main" java.lang.Error:
    Unresolved compilation problem:
    Type mismatch: cannot convert from int to String
    at program.Program.main(Program.java:8)

Compilers

For a compiler, the obvious approach to a ternary statement is to use the same code as an if-statement. Usually ternary statements have nearly the same performance as ifs.

Code style

To some developers, ternary statements make it harder to read code. If-statements are more expected, and may be easier to scan. I tend to avoid ternaries.