Answer 1

j -= 2 is a shortchut for j = j - 2

a = b is for assign value of variable 'b' to variable 'a'

a == b is for compare value of 'a' to value of 'b'... like an other exepression ( ie: a + b - c ), it produce a result ( like the return value of a function ). In case of comparison expression, the return value will be a 'boolean' with only value for 'true' and 'false'...

c = a == b would evaluate 'if a is equal to b' and assign the result ( true or false ) to variable 'c' ^^