Java Language Operators The Conditional Operator (? :)
Example
Syntax
{condition-to-evaluate} ? {statement-executed-on-true} : {statement-executed-on-false}
As shown in the syntax, the Conditional Operator (also known as the Ternary Operator1) uses the ? (question mark) and : (colon) characters to enable a conditional expression of two possible outcomes. It can be used to replace longer if-else blocks to return one of two values based on condition.
result = testCondition ? value1 : value2
Is equivalent to
if (testCondition) {
result = value1;
} else {
result = value2;
}
It can be read as “If testCondition is true, set result to value1; otherwise, set result to value2”.
For example:
// get absolute value using conditional operator
a = -10;
int absValue = a < 0 ? -a : a;
System.out.println("abs = " + absValue); // prints "abs = 10"
Is equivalent to
// get absolute value using if/else loop
a = -10;
int absValue;
if (a < 0) {
absValue = -a;
} else {
absValue = a;
}
System.out.println("abs = " + absValue); // prints "abs = 10"
Common Usage
You can use the conditional operator for conditional assignments (like null checking).
String x = y != null ? y.toString() : ""; //where y is an object
This example is equivalent to:
String x = "";
if (y != null) {
x = y.toString();
}
Since the Conditional Operator has the second-lowest precedence, above the Assignment Operators, there is rarely a need for use parenthesis around the condition, but parenthesis is required around the entire Conditional Operator construct when combined with other operators:
// no parenthesis needed for expressions in the 3 parts
10 <= a && a < 19 ? b * 5 : b * 7
// parenthesis required
7 * (a > 0 ? 2 : 5)
Conditional operators nesting can also be done in the third part, where it works more like chaining or like a switch statement.
a ? "a is true" :
b ? "a is false, b is true" :
c ? "a and b are false, c is true" :
"a, b, and c are false"
//Operator precedence can be illustrated with parenthesis:
a ? x : (b ? y : (c ? z : w))
Footnote:
1 - Both the Java Language Specification and the Java Tutorial call the (? :) operator the Conditional Operator. The Tutorial says that it is "also known as the Ternary Operator" as it is (currently) the only ternary operator defined by Java. The "Conditional Operator" terminology is consistent with C and C++ and other languages with an equivalent operator.
