Ternary Operator

The conditional operator, ?:, uses a boolean expression to determine which of two values to yield.

booleanExpression ? valueIfTrue : valueIfFalse

This is also called the ternary operator, since it has three operands.

• A boolean condition.
• A value to yield if the condition is true.
• A value to yield if the condition is false.

char status; // 'a' for adult, 'm' for minor
status = age >= 18 ? 'a' : 'm';

• This is similar to, but much more compact than:

if (age >= 18) {
  status = 'a';
}
else {
  status = 'm';
}

* Formatting can make ternary expressions easier to read.

status = ( age >= 18 ) ? 'a'
                       : 'm';

status = age >= 18
         ? 'a'
         : 'm';

?: is an operator that must yield a value:

status = age >= 18
         ? System.out.println("Adult")  // WILL NOT COMPILE
         : System.out.println("Minor"); // println() is a void method returning no value

• We must do something with the value returned by the ?: - either pass it to a method or assign it to a variable.

• The statement below yields a or m, but we don't do anything with that value.

    (age >= 18) ? (status = 'a') : (status = 'm');
    // WILL NOT COMPILE
    // "The left-hand side of an assignment must be a variable"
  

  That statement is as illegal as:

  'a'; // WILL NOT COMPILE
       // "The left-hand side of an assignment must be a variable"
  

Either of the two value expressions can include a ternary:

    status = ( age >= 18 )
             ? ( age >= 65 )
               ? 's'  // Senior
               : 'a'  // Adult
             : 'm';   // Minor

---

Prev -- Up -- Next