Question

I have incoming bits like, 0, 1, 11, 10 etc. Which I store in a string. Then I convert the string to an Int.

Now, suppose Int A = “011” and Int B = “00”. Is it possible in java to know, how many bits was there in the string which I have converted to the Int. Thanks.

Answer 1

Yes, just test each bit in turn using a mask. For integers there are 32 possible bits.

Luckily java provides this for you:

Integer.bitCount(value)

If you wanted to do it yourself:

int value = Integer.parseInt("1000101010", 2);

int bitCounter = 0;
for (int i = 0; i < Integer.SIZE; i++) {
    if (((1 << i) & value) > 0) {
        bitCounter++;
    }
}
System.out.println(value + " has " + bitCounter + " bits");

Output

554 has 4 bits

If alternatively you wanted the “length”, i.e. the number of 0s or 1s…

Convert to string and find length

System.out.println(Integer.toString(value, 2).length());

Use some knowledge of maths to take the base(2) log of the value.

double valueUnsigned;
if (value < 0) {
    valueUnsigned = (value & 0x7FFFFFF) + 0x80000000l;
} else {
    valueUnsigned = value;
}
System.out.println("Maths solution " + Math.floor(1d + Math.log(valueUnsigned) / Math.log(2)));