Java向左移动位时，溢出不会消失，但会在另一侧出现

Question

int i = 0x000000FF;
i = i << 24;

message = String.format("0x%08X", i);
// prints the message 0xFF000000

int i = 0x000000FF;
i = i << 32;

message = String.format("0x%08X", i);
// prints the message 0x000000FF

I was expecting the second one to print 0x00000000

What is going on?

Answer 1

See Java Language Specification 15.19. Shift Operators :

If the promoted type of the left-hand operand is int , then 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.

So, i << 32 is the same as i << 0 , ie no shift at all.