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What does ?false:true do/mean?

Angelo Tan

Joined: Oct 29, 2010
Posts: 10

I've encountered this piece of code many times already. I'm wondering what is it for? What does it do? And when should i use it?
Stephan van Hulst

Joined: Sep 20, 2010
Posts: 3598

Never, because they are pretty useless.

This is called the ternary operator. It consists of a boolean expression, followed by ?, followed by an expression, followed by :, and finally another expression.

If the boolean expression before the question mark evaluates to true, the operator returns the expression after the question mark. Otherwise, it returns the expression after the colon.
Here is an example:
This piece of code assigns to max either a or b, whichever is larger. The ternary operator has its uses. The reason your examples shouldn't be used, is because they simply return the outcome of the boolean expression before the question mark, or its inverse.
Jesper de Jong
Java Cowboy
Saloon Keeper

Joined: Aug 16, 2005
Posts: 14074

A line like this:

means exactly the same as this:

It's just a shorter syntax to write.

As Stephan noted, using "true" and "false" (or "false" and "true") for a and b is pretty useless...

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Angelo Tan

Joined: Oct 29, 2010
Posts: 10
thanks for the clear and thorough explanation.

got it now.
It is sorta covered in the JavaRanch Style Guide.
subject: What does ?false:true do/mean?
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