What does <<= operator mean in Java?

Question

Can you please explain this code snippet from HashMap constructor specifically the line

capacity <<= 1:

// Find a power of 2 >= initialCapacity
198         int capacity = 1;
199         while (capacity < initialCapacity)
200             capacity <<= 1;

Answer 1

It is equivalent to capacity = capacity << 1;.
That operation shifts capacity's bits one position to the left, which is equivalent to multiplying by 2.

The specific code you posted finds the smallest power of 2 which is larger than initialCapacity.

So if initialCapacity is 27, for example, capacity will be 32 (2^5) after the loop.