Question

I have to do Boolean operation like,

 B1=00 10 11 01 00 
 B2=00 10 11 01  
 B1 NOR B2 =11 11 11 11

How is it possible in Java ? Can anybody help ?

Sorry, I forgot to mention, is it possible in Java to perform this bit wise NOR operation from the left always without shifting (B2 has less bits) ?

Answer 1

If b1 and b2 are your (int) variables, the expression would be:

~(b1 | b2)

For more info, see Bitwise and Bit Shift Operators.

However, in your example the variables have different lengths. The result doesn’t correspond to a NOR either.

Update: if you have two sequences of boolean values, no equal size, and only need a portion of it (left to right), I’d suggest using a BitSet:

BitSet b1 = new BitSet();
// Fill it with booleans:
for ( int i = 0 ; i < myBooleans.length ; i++ )
    b1.set(i, myBooleans[i]);
// Or fill it with bytes:
BitSet b1 = BitSet.valueOf(myBytes);
// Or fill it with 0/1 from a string:
for ( int i = 0 ; i < myString.length() ; i++ )
    b1.set(i, myString.charAt(i) == "1");

BitSet b2 = new BitSet();
// Same as above

BitSet result = new BitSet();
result.or(b1); // Copies b1
result.or(b2); // Makes the OR
result.flip(0,result.size()); // Negates - the result is a NOR
result.clear(Math.min(b1.size(), b2.size()), result.size()); // Only retain the common size

If you really want to use int, then it’s better to represent it right to left (i.e. the first bit is b % 2, the second is b / 2 % 2, etc. Then you just have to do the NOR as explained in the beginning, and if necessary truncate the result.

If they are represented left to right, I believe a shift will be necessary (or a multiplication/division, which is essentially the same thing, but more expensive…), unless they are padded with 0’s (ex.: B1=0010 1101 0000 0000 0000 0000 0000 0000, B2=0010 1101 0000 0000 0000 0000 0000 0000). In this case you can do the operation normally.