See http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.19
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 value 0x1f (0b11111). The shift distance actually used is therefore always in the range 0 to 31, inclusive.
that is -1 >>> 32 is equivalent to -1 >>> 0 and -1 >>> 33 is equivalent to -1 >>> 1
and, especially confusing, -1 >>> -1 is equivalent to -1 >>> 31
