understanding java operator << [duplicate]

Question

This question already has answers here:

What does << mean in Java? (8 answers)

Closed 9 years ago.

i was working through the following oracle java class and came across this line of code:

public synchronized int getRGB() {
    return ((red << 16) | (green << 8) | blue);
}

I am lost as to what "<<" means, I also don't know what the return statement is suppose to return

Answer 1

It is a bit shift operation. Read more here. It will pack these 3 numbers into one integer.

Answer 2

24 bit colors are often represented as RRRRRRRRGGGGGGGGBBBBBBBB, with 8 bit values for each color. Your code takes the red value, shifts it 16 bits, shifts the green value 8 bits, and keeps the blue value unshifted, then performs a logical OR, which in this case is the same as adding the values. Think of it this way:

Your byte values for each color:

Red = 00011010
Green = 10101010
Blue = 11111111

The shifted values become:

Red << 16 = 
00011010 00000000 00000000
Green << 8 = 
00000000 10101010 00000000
Blue = 
00000000 00000000 11111111

The logical OR combines them into:

00011010 10101010 11111111

which is your 24 bit RGB value, which is returned.

Answer 3

public synchronized int getRGB() {
   return ((red << 16) | (green << 8) | blue);
}

I am lost as to what "<<" means, I also don't know what the return statement is suppose to return?

First off, the '<<' is called a bit shift operator. There is a fantastic write-up about them located here.

As to your second question, look at the signature of the method... it's going to return an int. BUT, in this case, it is going to return and int containing the value of blue and the bit shifted values of red and green.

Hope this helps!

Answer 4

x << y means "shift binary representation of x to left y places"

For instance

System.out.println(4 << 2);

will print 16.

4 is 100 in binary. If you shift 100 to the left 2 places, you get 10000 which is 16 in decimal.