Simple Histogram java class to calculate frequencies and display approximate histogram using the Unicode characters

Histogram.java

import static java.lang.Math.floor;
import static java.util.function.Function.identity;
import static java.util.stream.Collectors.groupingBy;
import static java.util.stream.Collectors.joining;
import static java.util.stream.Collectors.mapping;
import static java.util.stream.Collectors.summingInt;
import static java.util.stream.Collectors.toMap;
import static java.util.stream.IntStream.range;

import java.util.DoubleSummaryStatistics;
import java.util.List;
import java.util.Map;
import java.util.Random;
import java.util.stream.Collectors;
import java.util.stream.DoubleStream;

public class Histogram
{
    private static final String[] CHARACTERS = { "▁", "▂", "▃", "▅", "▆", "▇" };

    private List<Double> data;

    public Histogram(List<Double> data)
    {
        this.data = data;
    }

    private static Integer findBin(Double datum, int bins, double min, double max)
    {
        final double binWidth = (max - min) / bins;
        if ( datum >= max )
        {
            return bins - 1;
        }
        else if ( datum <= min )
        {
            return 0;
        }
        return (int)floor((datum - min) / binWidth);
    }

    public Map<Integer, Integer> histogram(int bins)
    {
        final DoubleSummaryStatistics statistics = this.data.stream()
            .mapToDouble(x -> x)
            .summaryStatistics();

        final double max = statistics.getMax();
        final double min = statistics.getMin();

        // Make sure that all bins are initialized
        final Map<Integer, Integer> histogram = range(0, bins).boxed()
            .collect(toMap(identity(), x -> 0));

        histogram.putAll(this.data.stream()
            .map(x -> x)
            .collect(groupingBy(x -> findBin(x, bins, min, max),
                mapping(x -> 1, summingInt(x -> x)))));

        return histogram;
    }

    public String toString(int bins)
    {
        final Map<Integer, Integer> frequencies = this.histogram(bins);
        final int maxFrequency = frequencies.values().stream()
            .mapToInt(x -> x).max().orElse(0);

        return frequencies.values().stream()
            .mapToDouble(x -> x / (double)maxFrequency)
            .mapToInt(x -> findBin(x, CHARACTERS.length, 0, 1))
            .mapToObj(x -> CHARACTERS[x])
            .collect(joining());
    }

    public static Histogram from(List<Double> data)
    {
        return new Histogram(data);
    }

    public static void main(String[] args) throws Exception
    {
        final Random random = new Random();
        List<Double> data = DoubleStream.generate(() -> random.nextGaussian())
            .limit(100000)
            .boxed()
            .collect(Collectors.toList());

        final Histogram historgram = Histogram.from(data);
        final Map<Integer, Integer> frequencies = historgram.histogram(11);

        System.out.println(frequencies);
        System.out.println(historgram.toString(11));
    }

}