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Why if
int x = -1 // binary: 11111111111111111111111111111111
x = x >>> 31;
we have 00000000000000000000000000000001
but if
int x = -1
x = x >>> 32;
we have 11111111111111111111111111111111 (again -1)
but not 00000000000000000000000000000000 ?
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In Java, bitwise operators perform operations on integer data at the individual bit-level. Here, the integer data includes byte , short , int , and long types of data. There are 7 operators to perform bit-level operations in Java.
This operator shifts the first operand the specified number of bits to the right. Excess bits shifted off to the right are discarded. Zero bits are shifted in from the left. The sign bit becomes 0 , so the result is always non-negative.
Difference between >> and >>> operator. Both >> and >>> are used to shift the bits towards the right. The difference is that the >> preserve the sign bit while the operator >>> does not preserve the sign bit. To preserve the sign bit, you need to add 0 in the MSB.
The Java programming language also provides operators that perform bitwise and bit shift operations on integral types.
From Section 15.19 of JLS:
If the promoted type of the left-hand operand is int, only the five lowest-order bits of the right-hand operand are used as the shift distance. It is as if the right-hand operand were subjected to a bitwise logical AND operator
&(§15.22.1) with the mask value0x1f (0b11111). The shift distance actually used is therefore always in the range0 to 31, inclusive.
Emphasis mine. So:
x >>> n
is equivalent to:
x >>> n & 0x1f // or x >>> n % 32
So, x >>> 32 is equivalent to x >>> 32 & 0x1f <==> x >>> 0 == x.
So the Rule of Thumb is, whenever you shift a number by a multiple of 32(int is 32 bits), you get back the same value.
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