What does "|=" mean? (pipe equal operator)

Solution 1:

|= reads the same way as +=.

notification.defaults |= Notification.DEFAULT_SOUND;

is the same as

notification.defaults = notification.defaults | Notification.DEFAULT_SOUND;

where | is the bit-wise OR operator.

All operators are referenced here.

A bit-wise operator is used because, as is frequent, those constants enable an int to carry flags.

If you look at those constants, you'll see that they're in powers of two :

public static final int DEFAULT_SOUND = 1;
public static final int DEFAULT_VIBRATE = 2; // is the same than 1<<1 or 10 in binary
public static final int DEFAULT_LIGHTS = 4; // is the same than 1<<2 or 100 in binary

So you can use bit-wise OR to add flags

int myFlags = DEFAULT_SOUND | DEFAULT_VIBRATE; // same as 001 | 010, producing 011

so

myFlags |= DEFAULT_LIGHTS;

simply means we add a flag.

And symmetrically, we test a flag is set using & :

boolean hasVibrate = (DEFAULT_VIBRATE & myFlags) != 0;

Solution 2:

You have already got sufficient answer for your question. But may be my answer help you more about |= kind of binary operators.

I am writing table for bitwise operators:
Following are valid:

----------------------------------------------------------------------------------------
Operator   Description                                   Example
----------------------------------------------------------------------------------------
|=        bitwise inclusive OR and assignment operator   C |= 2 is same as C = C | 2
^=        bitwise exclusive OR and assignment operator   C ^= 2 is same as C = C ^ 2
&=        Bitwise AND assignment operator                C &= 2 is same as C = C & 2
<<=       Left shift AND assignment operator             C <<= 2 is same as C = C << 2
>>=       Right shift AND assignment operator            C >>= 2 is same as C = C >> 2  
----------------------------------------------------------------------------------------

note all operators are binary operators.

Also Note: _{(for below points I wanted to add my answer)}

• >>> is bitwise operator in Java that is called Unsigned shift
  but >>>= not an operator in Java. >>>= operator

• ~ is bitwise complement bits, 0 to 1 and 1 to 0 (Unary operator) but ~= not an operator.

• Additionally, ! Called Logical NOT Operator, but != Checks if the value of two operands are equal or not, if values are not equal then condition becomes true. e.g. (A != B) is true. where as A=!B means if B is true then A become false (and if B is false then A become true).

_{side note: | is not called pipe, instead its called OR, pipe is shell terminology transfer one process out to next..}