// example code for: http://stackoverflow.com/a/21976027/616460
 
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
 
 
// the important bits are the implementations of next() below. everything
// else is (somewhat sloppy) code to support testing and output.
class Dist {
 
    // modify MAX_VALUE and RUN_COUNT as you see fit
    static final int MAX_VALUE = 30;
    static final int RUN_COUNT = 10000;
 
    static final Random random = new Random();
 
    // base class for a test; generates a set of RUN_COUNT random values
    // in the range [0, MAX_VALUE) and stores a histogram of the results.
    // subclasses should implement next() to return a value [0, MAXVALUE).
    static abstract class RandomTest {
        final int[] count = new int[MAX_VALUE];
        final String name;
        RandomTest (String name) { this.name = name; }
        RandomTest run () {
            System.out.println("Running " + name + "...");
            for (int n = 0; n < RUN_COUNT; ++ n) count[next()] ++;
            return this;
        }
        abstract int next ();
    }
 
    // Uniform distribution
    static class Uniform extends RandomTest {
        Uniform () { super("Uniform"); } 
        @Override int next () {
            return random.nextInt(MAX_VALUE);
        }
    }
 
    // pow(value, bias)
    static class Pow extends RandomTest {
        final double bias;
        Pow (double bias) { super("Pow(" + bias + ")"); this.bias = bias; }
        @Override int next () {
            double v = Math.pow(random.nextDouble(), bias);
            return (int)(v * MAX_VALUE);
        }
    }
 
    // [0,1) section of gaussian distribution, scaled by given value
    static class Gaussian extends RandomTest {
    	final double scale;
        Gaussian (double scale) { super("G(" + scale + ")"); this.scale = scale; }
        @Override int next () {
            double v;
            do {
                v = Math.abs(random.nextGaussian() / scale);
            } while (v >= 1.0);
            return (int)(v * MAX_VALUE);
        }
    }
 
    // cubic S
    static class Cubic extends RandomTest {
        Cubic () { super("Cubic"); }
        @Override int next () {
            double v = random.nextDouble();
            v = 3*v*v - 2*v*v*v;
            return (int)(v * MAX_VALUE);
        }
    }
 
    // print one row of results; prints header if index == -1
    static void printResultRow (List<RandomTest> tests, int index) {
        System.out.printf("%-5s:", (index < 0) ? "Name" : Integer.toString(index));
        for (RandomTest test:tests) {
            String s = (index < 0) ? test.name : Integer.toString(test.count[index]);
            System.out.printf("%9s ", s);
        }
        System.out.println();
    }
 
    // run all tests and print results    
    public static void main (String[] args) {
 
        List<RandomTest> tests = new ArrayList<RandomTest>();
        tests.add(new Uniform().run());
        tests.add(new Pow(0.5).run());
        tests.add(new Pow(2.0).run());
        tests.add(new Pow(20.0).run());
        tests.add(new Gaussian(1.0).run());
        tests.add(new Gaussian(3.5).run());
        tests.add(new Cubic().run());
 
        for (int n = -1; n < MAX_VALUE; ++ n)
            printResultRow(tests, n);
 
    }
 
}
 

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