Checking flag bits java

java bit-manipulation flags
Nagaraju picture Nagaraju · May 20, 2011 · Viewed 38.1k times · Source

I have a problem with flag bits. I have an int variable to hold flags. First I set some flags to that variable. Later I need check how many flags were set in that variable. But I don't know to do it.

Answer

pickypg picture pickypg · May 20, 2011

To check to see if a bit value is set:

int value = VALUE_TO_CHECK | OTHER_VALUE_TO_CHECK;

if ((value & VALUE_TO_CHECK) == VALUE_TO_CHECK)
{
    // do something--it was set
}

if ((value & OTHER_VALUE_TO_CHECK) == OTHER_VALUE_TO_CHECK)
{
    // also set (if it gets in here, then it was defined in 
    //   value, but it does not guarantee that it was set with
    //   OR without other values. To guarantee it's only this
    //   value just use == without bitwise logic)
}

It's important to note that you should not have a checked value as 0 unless it represents All or None (and don't use bitwise logic to compare; just use value == 0) because any value & 0 is ALWAYS 0.

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