In pages like http://en.wikipedia.org/wiki/?: the ternary/conditional operator ?:
seems to be used for conditional assignments. I tried to use it for method calling, like this:
(condition) ? doThis() : doThat();
Both methods return void. Java tells me it is not a statement.
So, I'm guessing I can't do conditional method calling... or can I?
Nope you cannot do that.
Nope, you can only assign values when doing ternary operations, not execute functions.
The conditional ternary operator in JavaScript assigns a value to a variable based on some condition and is the only JavaScript operator that takes three operands. result = 'somethingelse'; The ternary operator shortens this if/else statement into a single statement: result = (condition) ?
The conditional (ternary) operator is the only JavaScript operator that takes three operands: a condition followed by a question mark ( ? ), then an expression to execute if the condition is truthy followed by a colon ( : ), and finally the expression to execute if the condition is falsy.
Think of ternary operators like a method in this case. Saying a ? b : c
is (for the intents and purposes you're considering, see lasseespeholt's comment) equivalent to calling the pseudocode method:
ternary(a, b, c) if a return b else return c
which is why people can say things like x = a ? b : c
; it's basically like saying x = ternary(a, b, c)
. When you say (condition) ? doThis() : doThat()
, you're in effect saying:
if condition return doThis() else return doThat()
Look what happens if we try to substitute the methods for what they return
if condition return ??? else return ???
It doesn't even make sense to consider it. doThis()
and doThat()
don't return anything, because void
isn't an instantiable type, so the ternary
method can't return anything either, so Java doesn't know what to do with your statement and complains.
There are ways around this, but they're all bad practice (you could modify your methods to have a return value but don't do anything with what they return, you could create new methods that call your methods and then return null, etc.). You're much better off just using an if
statement in this case.
EDIT Furthermore, there's an even bigger issue. Even if you were returning values, Java does not consider a ? b : c
a statement in any sense.
The ternary operator is simply syntactic sugar.
It makes code easier to read/write, but it does not add real functionality.
Its primary use was to compress several lines of code into a single line, and was very useful when building Strings that differ only slightly, based on some conditions.
eg.
Collection<?> col = ... System.out.println("There " + (col.size()==1 ? "is" : "are") + " " + col.size() + " " + (col.size()==1 ? "element" : "elements") + " in the collection");
instead of
Collection<?> col = ... String message = "There "; if(col.size()==1) message += "is"; else message += "are"; message += " "+col.size() if(col.size()==1) message += " element"; else message += " elements"; message += " in the collection"; System.out.println(message);
As you can see, it simplifies the code.
(note: In the second example it is better to use StringBuilder
instead of String concatenation)
But since (condition) ? doThis() : doThat();
(without return values) has the same meaning as if(condition) doThis(); else doThat();
there would be two ways of writing the same thing, without adding functionality. It would only complicate things:
void
methodsSo No, the ternary operation can not be used for conditional method calling. Use if-else instead:
if(condition) doThis(); else doThat();
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