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  1. #1
    357mag is offline Member
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    May 2010
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    Default The increment operator with parentheses

    Look at this:

    Java Code:
    x = 10
    y = 2
    z = x++ - (x * y)
    What I first did was do what was in parentheses first (cuz that's what we're taught), since parentheses have higher precedence than the ++ operator. So first I multiplied
    (10 * 2) to get 20. Then I plugged 10 in for x and thought it would evaluate to
    z = 10 - 20 which would result in -10 (final value of x would be 11 after this statement executed.)

    But I got it wrong. I guess the proper way to handle this is first increment x from 10 to 11. Then plug the new value 11 in where x is in the parentheses so you now have
    z = 10 - (11 * 2) which results in -12.

    I don't quite follow. Why doesn't the compiler first evaluate what is in parentheses? Since parentheses have a higher order of precedence anyway it seems to me the compiler would first multiply 10 * 2 to get 20.

  2. #2
    Norm's Avatar
    Norm is offline Moderator
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    Jun 2008
    Eastern Florida
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    Personally I would never write code where there can be a confusion over what happens first.
    Break the statement up into separate statement that are understandable and easy to follow.

  3. #3
    Fubarable's Avatar
    Fubarable is offline Moderator
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    Jun 2008
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    • Precedence rules matter when two operators share the same operand.
    • Order of evaluation. In Java, the left operand is always evaluated before the right operand. Also applies to function arguments.
    • The left-hand operand of a binary operator appears to be fully evaluated before any part of the right-hand operand is evaluated

    see: 15.7.1 Evaluate Left-Hand Operand First

    But I agree with Norm: that code should be taken out back and shot.

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