Confused by java syntax

 

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  • Shortcut “or-assignment” (|=) operator in Java 8 answers

    • 这是对声明的简短陈述： 

    noti.flags = noti.flags | Notification.FLAG_AUTO_CANCEL;

    It's a Bitwise OR operator used as assignment 

    noti.flags |= Notification.FLAG_AUTO_CANCEL;

    is the same of 

    noti.flags = noti.flags | Notification.FLAG_AUTO_CANCEL

    It's the assignment version of the Bitwise Or operator, ie: 

     noti.flags = noti.flags | Notification.FLAG_AUTO_CANCEL;

    The bitwise or does an inclusive bitwise OR operation: 

    10110 bitwise or
01100
-----------------
11110

    From the source code:

    Bit to be bitwise-ored into the flags field that should be set if the notification should be canceled when it is clicked by the user. 

    public static final int FLAG_AUTO_CANCEL = 0x00000010;

    This is hexadecimal for the number 16. If you're wondering why we use these types of flags, it's because other flags will have representations: 

     0x00000020
 0x00000040
 0x00000080

    Each time, we go up by a power of 2. Converting this to binary, we get: 

     00010000
 00100000
 01000000
 10000000

    Hence, we can use a bitwise or to determine which of the flags are present, since each flag is contains only one 1 and they are all in different locations.

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