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Got a practice question, and I have the below code:

while (false) { x=3; }

The x=3 is unreachable code, and I don't really understand why. There is a similar section of code:

if (false) { x=3; }

which is perfectly valid.

May be a bit of a noob question, or may be I'm just missing something, but if you could help me understand why that'd be great, thanks!

I am asking specifically about the difference between the if and while statement, because the same line of code changed to if, is valid and will compile.

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  • Code is unreachable means the compiler deemed it that there cannot be no path to statement x=3; because while ( false )can never be true Commented Aug 9, 2016 at 11:32
  • The kicker is: neither can if(false). The real question is: why does the compiler not have problems with the if statement. Commented Aug 9, 2016 at 11:34
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    And for the second part of the question, refer to stackoverflow.com/a/8570302/1743880 Commented Aug 9, 2016 at 11:34
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    And refer to stackoverflow.com/questions/20299914/… also Commented Aug 9, 2016 at 11:35
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    Please refer to the above questions also. They explain this behaviour both for if and while statements, by referencing the Java specification. See stackoverflow.com/questions/20299914/… Commented Aug 9, 2016 at 11:37

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Read below article it will answer your question: http://docs.oracle.com/javase/specs/jls/se7/html/jls-14.html#jls-14.21

while statement can complete normally iff at least one of the following is true:

o The while statement is reachable and the condition expression is not a constant expression (§15.28) with value true.

o There is a reachable break statement that exits the while statement.

The contained statement is reachable iff the while statement is reachable and the condition expression is not a constant expression whose value is false.

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