CODEWITHSUNDEEP
javahashmapbit-manipulationbit
Geek
Geek

Reputation: 27193

What does <<= operator mean in Java?

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;

Upvotes: 5

Views: 331

Answers (4)

Nitish Pareek
Nitish Pareek

Reputation: 2513

every time this comes out of the loop the value of 'capacity' goes 2 raised by a power higher.

like initially it is 1 i.e.2^0; the operation(capacity <<= 1) for the first time makes it 2^1 and then 2^2 and so on. May be you would like to see the more on it at http://www.tutorialspoint.com/java/java_basic_operators.htm

Upvotes: 0

assylias
assylias

Reputation: 328598

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.

Upvotes: 11

Romain
Romain

Reputation: 12819

Just like var += 1 is about equivalent to var = var + 1, what you see here (var <<= 1) is about equivalent to var = var << 1, which is "set var to be the result of a 1-position binary left-shift of var."

In this very specific case, it's actually a slightly (runtime) faster way of expressing capacity *= 2 (because a bitwise left-shift of 1 position is equivalent to a multiplication by 2).

Upvotes: 4

Kuba Wyrostek
Kuba Wyrostek

Reputation: 6221

It is equivalent of

capacity = capacity << 1;

which shifts bits in capacity one position to the left (so i.e. 00011011 becomes 00110110).

Upvotes: 3

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