Learn Java: Keep it brief with Java's ternary operator

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Keep it brief with Java's ternary operator

Introduction

Interested in saying a lot while writing a little? In a single line of code, Java's ternary operator let's you assign a value to a variable based on one or more boolean decisions. Think of this operator as a potential alternative to the if-then-else syntax.
Although it may be a little confusing when you first see it, the ternary operator lets you make powerful decisions with a minimal amount of coding.

A sample min/max comparison

A common use of the ternary operator (also called the conditional operator) is to assign the minimum (or maximum) value of two variables to a third variable, essentially replacing a Math.min(a,b) or Math.max(a,b) method call.

The ternary code that assigns the minimum of two variables, a and b, to a third variable named minVal is:

// code to assign the minimum value

minVal = (a < b; a ? b);

In this code, if the variable a is less than b, minVal is assigned the value of a; otherwise, minVal is assigned the value of b. Note that the parentheses in this example are optional, but I use them to improve the readability of the code.

Also notice that the ternary operator is an expression that returns a value based on the conditional phrase it evaluates. This is different than the if-then-else syntax, which executes a statement block based on it's conditional phrase.

In performance tests on a Sun Solaris workstation, the ternary operator was four times faster than the Math.min() method when comparing float variables, and twice as fast when comparing integer variables. In similar cases in your code, I recommend testing to determine if performance improvements can be achieved. As the old saying goes, your performance may vary.

Other ternary uses

In the ternary decision-making process, once a decision is made, you can return anything you want. In the case of a law-enforcement officer algorithm, the following code compares two numeric values and returns a boolean, to decide who gets a speeding ticket:

boolean giveTicket;

giveTicket = speed > speedLimit ? true : false;

if (giveTicket)

pullEmOver(); // nab the offender!

Knowing that the ternary operator returns a true/false value in this example, you can make the code even more concise by embedding the ternary operation into the if-then statement:

if (speed > speedLimit ? true : false;)

pullEmOver();

Of course, in the interests of readability and maintainability, each developer (or development staff) must decide what is readable and what is not, and this example might go too far for many developers.

As a final example, note that the comparison portion of the ternary operator can contain complex if-then comparisons. The following code for a self-controlled car makes a fairly complex decision about when to stop, based on a series of boolean values:

// declare some boolean variables

boolean stopCar, lightIsRed, trafficIsStopped,

outOfGas, wallInFront;

// ... other code activity here ...

// decide when to stop the car
stopCar = lightIsRed || trafficIsStopped ||
outOfGas || wallInFront ? true : false;

In this case, if a traffic light is red, or traffic is stopped, or we're out of gas, or there's a wall in front of us, we should set stopCar to true. If not, just keep driving.

Conclusion

Once you get used to the slightly unusual syntax, the ternary operator can help you make powerful decisions with a minimal amount of coding. I find that it's a perfect fit where short true/false decisions lead to the assignment of a value to a single variable. You'll also find this operator in the source code of the class libraries of many vendors, so it's good to have at least a modest understanding of this unusual operator.

Note: This article first appeared in ZD Journals JBuilder Journal, and is reprinted here with their permission. The article author now works at Developer's Daily.

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