Weird result of Java Integer left shift

As per the Java Language Specification 15.19. Shift Operators (slightly paraphrased):

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 & with the mask value 0x1f ,or 0b11111. The shift distance actually used is therefore always in the range 0 to 31, inclusive.

That means that (for example) 33, being the 6-bit binary 100001, is reduced to the 5-bit 00001 before being used. So x << 33 is identical to x << 1.