Histogram.java

Below is the syntax highlighted version of Histogram.java from §3.2 Creating Data Types.

/******************************************************************************
 *  Compilation:  javac Histogram.java
 *  Execution:    java Histogram n trials
 *
 *  This data type supports simple client code to create dynamic
 *  histograms of the frequency of occurrence of values in [0, n).
 *  The frequencies are kept in an instance-variable array, and
 *  an instance variable max tracks the maximum frequency (for scaling).
 *
 *  % java Histogram 50 1000000
 *
 ******************************************************************************/

public class Histogram {
    private final double[] freq;   // freq[i] = # occurrences of value i
    private double max;            // max frequency of any value

    // Create a new histogram.
    public Histogram(int n) {
        freq = new double[n];
    }

    // Add one occurrence of the value i.
    public void addDataPoint(int i) {
        freq[i]++;
        if (freq[i] > max) max = freq[i];
    }

    // draw (and scale) the histogram.
    public void draw() {
        StdDraw.setYscale(-1, max + 1);  // to leave a little border
        StdStats.plotBars(freq);
    }

    // See Program 2.2.6.
    public static void main(String[] args) {
        int n = Integer.parseInt(args[0]);       // number of coins
        int trials = Integer.parseInt(args[1]);  // number of trials

        // create the histogram
        Histogram histogram = new Histogram(n+1);
        for (int t = 0; t < trials; t++) {
            histogram.addDataPoint(Bernoulli.binomial(n));
        }

        // display using standard draw
        StdDraw.setCanvasSize(500, 100);
        histogram.draw();
    }
}