Question

For example:

WakeLock wakeLock = powerManager.newWakeLock(PowerManager.FULL_WAKE_LOCK|
        PowerManager.ACQUIRE_CAUSES_WAKEUP|PowerManager.ON_AFTER_RELEASE, "Alarm");

What does the ‘ | ‘ character mean?

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More details about the problem:

I’m asking this because when I instantiate the wakelock with only PowerManager.AQUIRE_CAUSES_WAKEUP the program stops working, where as when I use the way above, it works fine.

I’m wondering if the cause of this is because the program ignore the ACQUIRE_CAUSES_WAKEUP tag and it ends up not being used.

Answer 1

In general, that symbol (|) is a bitwise OR. It’s used in a lot of different languages and environments outside of Android.

It’s usage is:

“X|Y : if X or Y is 1, then the result is 1”

In your specific case it’s being used to create a bit field. Besure to review the Android power manager code base here.

Possible flags for this API are:

PARTIAL_WAKE_LOCK        = 0x01 
SCREEN_DIM_WAKE_LOCK     = 0x06
SCREEN_BRIGHT_WAKE_LOCK  = 0x0a
FULL_WAKE_LOCK           = 0x1a

These are mutually exclusive (you can only pick one), but you can “OR in” some other flags:

ON_AFTER_RELEASE         = 0x20000000
ACQUIRE_CAUSES_WAKEUP    = 0x10000000

So once your code runs it ORs these flags together resulting in:

    0x20000000
  | 0x10000000
  | 0x0000001a
---------------
    0x3000001a

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I’m asking this because when i instantiate the wakelock with only “PowerManager.AQUIRE_CAUSES_WAKEUP” the program stops working

That’s because you have to pick one of the levels of wake lock (PARTIAL, SCREEN_DIM, SCREEN_BRIGHT, or FULL), you’re trying to run with just one of the optional wake lock flags…