I was learning about assignment operators in Java in W3schools. But I didn't get what these two operators mean?
These are examples of assignment operators. Essentially, they both perform the arithmetic operation on a variable, and assign its result to that variable, in a single operation. They're equivalent to doing it in two steps, for the most part:
int a = 23;
int b = 2;
a += b; // addition - same as `a = a + b`
a -= b; // subtraction
a *= b; // multiplication
a /= b; // floor division
a %= b; // modulo division
a &= b; // bitwise and
a |= b; // bitwise or
a ^= b; // bitwise xor
a >>= b; // right bitshift
a <<= b; // left bitshift
The bitshift operations in particular are the ones you're asking about. They take the binary representation of a number, and shift it left or right by the given number of places, filling in missing spaces with zeroes. For example, the binary representation of 23 is 00010111.
So, 23 << 2 would be equal to 01011100, or 92; whereas 23 >> 2 would be equal to 00000101, or 5.
You could also think of it as doing integer multiplication or division using powers of two:
a << b will generally produce the same result as a * Math.pow(2, b)a >> b will generally produce the same result as a / Math.pow(2, b)