Binary In Java

[GiantEnemyCrab]

Hi, I'm new here, and I have one doozy of a code.
Basically It involves binary, which I have little knowledge on how to do in java. It's a very roundabout code, but basically :

a hypothetical multi-touch device encodes information in 64-bit long integers. The values of up to 3 contact points -- (x1,y1), (x2,y2), (x3,y3) -- are recorded as well as the corresponding pressures -- p1, p2, p3.
The number of points reported, n, will be between 0 and 3 and is represented with 2 bits. The touch pad is wider than it is tall, so the x values are reported with 9 bits to give values between 0 and 511. The y values are reported with 7 bits to give values between 0 and 255. Pressure values are reported with 3 bits to give values between 0 and 7.

So this is a 2-parter, the first being a relatively simple CONCEPT. I must
A)Write a method that takes integers, representing x, y and p, and make a 64bit long integer. I’ll have 3 different methods, one for 1 contact point, 1 for 2 contact points, and 1 for 3 contact points. That way I’ll know what automatically what value to use for n.
B) Given a very 64bit integer, I’ll have a code that’ll ask for any of the x1, y1, x2, y2, x3 or y3, and I must supply them with it.

It’s pretty much the concept of the binary that’s throwing me off, really.

[ComputerJy]

So. What's your question?
Hopefully its not "Would you do my homework for me?"

[GiantEnemyCrab]

No, I wouldn't expect anyone to do that for me, this is my work,I just need a little push in the right direction.

The long is 64 bits.
bits 0- 1, how many contact points.
bits 2- 3, unused
bits 4-12, x1
bits 13-20, y1
bits 21-29, x2
bits 30-37, y2
bits 38-46, x3
bits 47-54, y3
bits 55-57, p1
bits 58-60, p2
bits 61-63, p3.


Right now I'm figuring out how to do
public static long makeStatusWord(int x1, int y1, int p1), where this method only has one contact point. I have to turn the 3 integers I've gotten into one 'long', along with the first two bits saying that only 1 contact point was made. The rest should all come out as 0's.

That is, I BELIEVE that long is binary.
I guess I'm mostly confused about 'masks'

EDIT: I've already figured out how to take each part and move it to the right spot, using the << method
So something like L = n & x<< 4 & y<<13 & p<< 55.

[ComputerJy]

Still no question. Anyway your code should look something like

	public static void main(final String[] args) {
		final int x1 = 12, x2 = 12, x3 = 12, y1 = 12, y2 = 12, y3 = 12, p1 = 7, p2 = 7, p3 = 7;
		long value;
		value = (((long) p3 << 61) & 0xFFFFFFFFFFFFFFFFL);
		value = (value | ((long) p2 << 58) & 0xFFFFFFFFFFFFFFFFL);
		value = (value | ((long) p1 << 55) & 0xFFFFFFFFFFFFFFFFL);
		value = (value | ((long) y3 << 47) & 0xFFFFFFFFFFFFFFFFL);
		value = (value | ((long) x3 << 38) & 0xFFFFFFFFFFFFFFFFL);
		value = (value | ((long) y2 << 30) & 0xFFFFFFFFFFFFFFFFL);
		value = (value | ((long) x2 << 21) & 0xFFFFFFFFFFFFFFFFL);
		value = (value | ((long) y1 << 13) & 0xFFFFFFFFFFFFFFFFL);
		value = (value | ((long) x1 << 4) & 0xFFFFFFFFFFFFFFFFL);
		value = (value & 0xFFFFFFFFFFFFFFF3L); // Set the unused bits to 0s
		value = value | 3L;
		System.out.println(Long.toHexString(value));
	}

And if you want to learn more about bitwise operations visit http://www.java2s.com/Tutorial/Java/...-Operators.htm

[GiantEnemyCrab]

Wow, the site's really helpful, and I guessed I should have posted I figured out that part afterwards, though seeing that shows I need one or two adjustments.....

Well, here's a completely legit question. For the next part, we must take out parts from a long and return an int. For example, it wants the integer value of x2. I know how to extract it, I just forgot how to turn it from long to int.

    public static int numberOfPoints(long statusWord){
    	int n = statusWord & 0x2; //type mismatch error
    	return n;
    }

EDIT: Nvm, I seem to be too quick in jumping to asking people. I got it.

 public static int numberOfPoints(long statusWord){
    	long n = statusWord & 0x2;
    	int nint = (int)n;
    	return nint;
    }

[ComputerJy]

Good for you my friend. You're always welcome to ask.
If you're done here please don't forget to mark the thread resolved from the Thread tools menu

[GiantEnemyCrab]

There's a second part of it which I've yet to do, so it's not done completely.

Also, I'm relooking at your code you posted
value = (value & 0xFFFFFFFFFFFFFFF3L); // Set the unused bits to 0s
value = value | 3L;
I don't get why the 3 is there..... from what i count, that makes 75.......

[ComputerJy]

the first 3 is set to clear bits 2-3 (unused) and the second one is.. Well I assumed you'll always have 3 contact points