Java + bitwise operation

Question

Hi All,

I have a long variable in java and am converting it to a binary string, like

long var = 24; Long.toBinaryString(val);

Now this prints only 7 bits, but I need to display all the 64 bits, i.e. all the leading zeros also, how can I achieve this?

The reason is I need to iterate through each bit and perform an operation according to the status, is there a better way to do it?

Answer 1

Yes, there's an easier way to do it. You could have a for loop where you test the 0 bit, then shift everything right. You can test the 0 bit with an expression like 1 & var, then use >> to shuffle the remaining bits to the right.

Answer 2

Yes, see http://java.sun.com/docs/books/tutorial/java/nutsandbolts/op3.html for information on bitwise operations.

Otherwise use the Formatter: http://java.sun.com/j2se/1.5.0/docs/api/java/util/Formatter.html

Answer 3

You can use binary operators to access the individual bits of an long. The following code prints the individual bits of "i" as "true" or "false".

long i = 1024;
for(int n = 63; n >= 0; n--)
    System.out.println(n + ": " + ((i & (1L << n)) != 0));

Answer 4

Not sure, but I think it should go like this:

int i=0, thisbit;
mask = 1;
while (i++ < 64)
{
    thisbit = var & mask;
    // check thisbit here...
    //
    var = var >>> 1;
    mask*=2;
}

Answer 5

If you want to iterate through the bits, you might be better off testing each bit without converting it to a string:

if ((val & (1L << bitPosition)) != 0)
    // etc

But, if you truly want a binary string, this is the easiest way to left-pad it with zeros:

string padding = "0000000000000000000000000000000000000000000000000000000000000000";
string result = padding + Long.toBinaryString(val);
result = result.substring(result.length() - 64, result.length());  // take the right-most 64 digits

Answer 6

This will work;

String s =  Long.toBinaryString(val);
while (s.length() < 64)
{
    s = "0" + s;
}

If you want to do this with a StringBuffer, so;

StringBuffer s =  new StringBuffer(Long.toBinaryString(val));
while (s.length() < 64)
{
    s.insert(0, "0");
}
String str = s.toString();