import java.util.*;
import java.awt.*;

// A class to hold an (x,y) pair where both are double's.
class Pointd {
    double x, y;
}


public class Histogram2D {

    public static void main (String[] argv)
    {
        // Number of points to generate.
	int numSamples = 1000;
	Pointd[] points = new Pointd [1000];

        // Generate random points from a Gaussian distribution
        // where both x and y are in the range [0,4].
	for (int n=0; n<numSamples; n++) {
	    points[n] = nextGaussian ();
	}
        
        // Compute and print the histogram.
	Integer[][] gaussianHist = makeHistogram (points);
	print (gaussianHist);

        // Do the same for points generated from a uniform distribution.
	for (int n=0; n<numSamples; n++) {
	    points[n] = nextUniform ();
	}
	Integer[][] uniform = makeHistogram (points);
	print (uniform);
    }


    static void print (Integer[][] H)
    {
	System.out.println ("Histogram ");
	for (int i=0; i<H.length; i++) {
	    for (int j=0; j<H[i].length; j++) {
                // Note: use of printf for formatting.
		System.out.printf (" %3d", H[i][j]);
	    }
	    System.out.println ();
	}
    }

    
    // Class Random is in java.util.
    static Random rand = new Random ();

    static Pointd nextGaussian ()
    {
	Pointd p = new Pointd ();

	// Generate x value.
	double x = rand.nextGaussian ();
	while ( (x <= -2) || (x >= 2) ) {
	    x = rand.nextGaussian ();
	}
	p.x = x + 2;

	// Generate y value.
	double y = rand.nextGaussian ();
	while ( (y <= -2) || (y >= 2) ) {
	    y = rand.nextGaussian ();
	}
	p.y = y + 2;

	return p;
    }

    static Pointd nextUniform ()
    {
	Pointd p = new Pointd ();

        // Random.nextDouble() generates between 0 and 1. We will
        // scale by 4 to create a point in the interval [0,4].
	p.x = 4 * rand.nextDouble ();
	p.y = 4 * rand.nextDouble ();

	return p;
    }


    static Integer[][] makeHistogram (Pointd[] points)
    {
        // Size of histogram.
	int size = 10;

        // Make the space for it, using instances of java.lang.Integer.
	Integer[][] hist = new Integer [size][size];

        // Initialize: must create an instance.
	for (int i=0; i<size; i++) {
	    for (int j=0; j<size; j++) {
		hist[i][j] = new Integer (0);
	    }
	}

        // Size of each cell.
	double interval = 4.0 / size;

        // Now count.
	for (int n=0; n<points.length; n++) {
	    int i = (int) (points[n].x / interval);
	    int j = (int) (points[n].y / interval);

            // Note: increment operator works for Integer's.
	    hist[i][j] ++;
	}

	return hist;
    }

}