What is the /= operator in Java?

It is an abbreviation for x = x / y (x /= y). What it does is it divides the variable to be asigned by the left hand side of it and stores it in the right hand side. You can always change:

x = x / y

to

x /= y

You can do this with most other operators like * / + and -. I am not sure about bitwise operators though.

a/=b; implies that divide a with b and put the result into a

It's a combination division-plus-assignment operator.

a /= b;

means divide a by b and put the result in a.

There are similar operators for addition, subtraction, and multiplication: +=, -= and *=.

%= will do modulus.

>>= and <<= will do bit shifting.