java - Why are values in the OpenJDK implementation of HashMap (and other classes) initialized using bitshifts?

Question

I was looking at OpenJDK's implementation of HashMap and stumbled upon this line of code where the default initial capacity is set:

static final int DEFAULT_INITIAL_CAPACITY = 1 << 4; // aka 16

Why is a bitshift used here instead of just initializing DEFAULT_INITIAL_CAPACITY with 16? I've looked at other classes like Arrays and there, too, a value is initialized with a bitshift:

private static final int MIN_ARRAY_SORT_GRAN = 1 << 13;

Is it a conventional thing or is it more important for someone working with these implementations to know which binary number the values are instead of the decimal representation?

question from:https://stackoverflow.com/questions/65846183/why-are-values-in-the-openjdk-implementation-of-hashmap-and-other-classes-init

Answer 1

Because sometimes it's easier to reason with number of bits, rather than numerical ranges. In the case of HashMap, however, another reason is that you need to do hash % numberOfBuckets, the modulo operation is expensive, so to fasten up one can use a power of two, then modulo may be replaced with logical AND - it'll do the same, but works that way only for powers of two. The Arrays case - may be similar reasons.