Why is there no unsigned left-shift operator in Java [closed]

Question

I have the following code:

int a = -1;
System.out.println(a<<1);

This prints -2. That means the sign-bit is preserved. There is no unsigned left-shift operator in Java. My question is, what if you want to push off the sign-bit, as when you are using an int not to store a value, but to contain a pattern of bits that represent something?

Answer 1

The reason this prints -2 is not that the sign of -1 gets preserved, but that the bit at position 31 which gets shifted into position 32 happens to be 1 as well. In other words, the sign after shifting left by one is determined by the value of the second highest bit.

Binary representation of -1 has 1s in all bits (an explanation can be found here), so the result remains negative as you continue shifting the number, until you shift out the last 1 bit after 32 shifts.

If you would like to drop the sign, you can mask the result to make it positive.

Why is there no unsigned left-shift operator in Java

Unlike shifting right, when the shift operator needs to make a decision on what to shift into the vacated position of the most significant bit, the value being shifted left determines the value of the new sign bit. The new zero bit is shifted into the least significant position, which does not have any special meaning.