Condition evaluation process in Java

Question

Lets say I have the following condition:

if ( myList == null || myList.isEmpty() || xomeX == someY )

What is the order of the evaluation of these conditions? Left or right, right to left or random each time?

If the first one passes, then the others are ignored?

Left to right i guess :) yes other will be ignored – usman allam Jul 29 '13 at 12:22 — usman allam, Jul 29 '13 at 12:22

score 28 · Accepted Answer · edited Jun 20 '20 at 09:12

28

It should be always be left to right except the assignment operator = . You are using short circuit OR operator , hence if the first condition is true , rest of them won't be evaluated.

JLS 15.24:

The conditional-or operator is syntactically left-associative (it groups left-to-right).

At run time, the left-hand operand expression is evaluated first; if the result has type Boolean, it is subjected to unboxing conversion (§5.1.8).

If the resulting value is true, the value of the conditional-or expression is true and the right-hand operand expression is not evaluated.

edited Jun 20 '20 at 09:12

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answered Jul 29 '13 at 12:21

AllTooSir

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"except the assignment operator `=`". The left operand of the assignment operator is evaluated before the right operand as well. – sepp2k Jul 29 '13 at 12:32
@sepp2k How this should be evaluated : `x=y=z+1;` ! – AllTooSir Jul 29 '13 at 12:40
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First `x` is evaluated, then `y`, then `z`, then `1`, then `valueOfZ +1`, then `y = resultOfZPlus1`, then `x = resultOfAssigningY`. – sepp2k Jul 29 '13 at 12:43

Vincent van der Weele · Answer 2 · 2013-07-29T12:30:33.377

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From the JLS

At run time, the left-hand operand expression is evaluated first [...] If the resulting value is true, the value of the conditional-or expression is true and the right-hand operand expression is not evaluated.

edited Jul 29 '13 at 12:30

answered Jul 29 '13 at 12:23

Vincent van der Weele

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Associativity is irrelevant to the order in which the operands are evaluated. – sepp2k Jul 29 '13 at 12:26
@sepp2k You're right, I better remove that part – Vincent van der Weele Jul 29 '13 at 12:32

score 7 · Answer 3 · edited May 23 '17 at 11:54

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if ( myList == null || myList.isEmpty() || xomeX == someY )

Yes the evaluation is from left to right!

and

If the first condition is true next condition is not evaluated. This concept is called Short-circuit evaluation. You can read more on this here. Similar SO question posted earlier is Java logical operator short-circuiting

edited May 23 '17 at 11:54

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answered Jul 29 '13 at 12:34

Aniket Thakur

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score 3 · Answer 4 · answered Jul 29 '13 at 12:21

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1) left to right

2) in this case, if one condition is true, it doesn't evaluate the rest. so if myList is null, it won't throw a NullPointerException evaluating myList.isEmpty() (because it won't evaluate it)

answered Jul 29 '13 at 12:21

morgano

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score 1 · Answer 5 · answered Jul 29 '13 at 12:44

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Every operator has its own precedence and associativity.

These links are enough to answer your question.

answered Jul 29 '13 at 12:44

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score 0 · Answer 6 · answered Jul 29 '13 at 12:28

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|| is the short-circuit OR operator, that means that conditions are strictly evaluated from left to right, and this checking process stops on first true result.

answered Jul 29 '13 at 12:28

AlexeyGorovoy

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Condition evaluation process in Java

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