Right shift operators

[Satyajeet Kadam]

Hi i get confused when it comes to shift operator

System.out.println(-1>>>2);
System.out.println(-1>>2);

From my understanding
Number to be shifted is always left operand
the number of bits to be shifted is always right operand
In this your number of bits to be shifted is greater thn actual number
so we use formulae
32%2=0 then we use 0>>>2 and 0>>2= 0/2pow2=0
0 is my ans
but when i compile and run the application i get following ans

1073741823
-1

Please explain me where i have gone wrong

[marc weber]

Originally posted by amolpalekar kadolkar:
...In this your number of bits to be shifted is greater thn actual number
so we use formulae
32%2=0 then we use 0>>>2 and 0>>2= 0/2pow2=0
0 is my ans...

I think what you're looking for is something like: If the amount of the shift (the right-hand operand) is greater than the number of bits in the type (32 for int, or 64 for long), then shift by the remainder after division by the number of bits in the type.

For example, if x is an int, then for x >>> 35, you would use x >>> (35%32), which is x >>> 3.

Technically, for int shifting, only the last 5 bits of the right-hand operand are used, so the shift will always be between 0 and 31 inclusively (even if the right-hand operand is negative). For long shifting, only the last 6 bits of the right-hand operand are used, so the shift will always be between 0 and 63 inclusively.

Also, note that bit shifting is on the 1.4 exam, but not on the 1.5 exam.

[Cheryl Gray]

I know that with the 2nd one (-1 >> 2) should give -1...ie.
(-1 >> a number = -1)

[Cheryl Gray]

Also, for the 1st one, (-1>>>2) I know that the answer will be a positive number since the >>> produces a sign change if the number, in this case
(-1), is a negative number.

[marc weber]

Originally posted by Cheryl Gray:
Also, for the 1st one, (-1>>>2) I know that the answer will be a positive number since the >>> produces a sign change if the number, in this case (-1), is a negative number.

Unless the shift distance (the right operand) is divisible by the number of bits in the (possibly widened) type of the left operand. In that case, the result will be -1, because the shift distance will be zero.

Again, don't worry about this if you're studying for 1.5.