[Java] Cryptanalysis - Coincidence Counting

Code:
import javax.swing.JFrame;

import org.jfree.chart.ChartFactory;

import org.jfree.chart.ChartPanel;

import org.jfree.chart.JFreeChart;

import org.jfree.chart.plot.PlotOrientation;

import org.jfree.data.category.DefaultCategoryDataset;



public class CoincidenceCount implements Analysis {



    private int maxShift;



    @Override

    public String analyse(String code) {

        maxShift = code.length() - 1;

        int[] count = new int[maxShift + 1];



        for (int i = 1; i <= maxShift; i++) {

            String shifted = shiftText(code, i);

            count[i] = coincidenceCount(shifted, code);

        }

        createBarChart(count);

        return countString(count);

    }



    private String shiftText(String code, int shift) {

        StringBuilder b = new StringBuilder();

        b.append(code.substring(shift));

        b.append(code.substring(0, shift));

        return b.toString();

    }



    private String countString(int[] count) {

        StringBuilder b = new StringBuilder();

        b.append("shift\tcoincidences\n");

        for (int key = 1; key <= maxShift; key++) {

            b.append(key + "\t" + count[key] + "\n");

        }

        return b.toString();

    }



    private int coincidenceCount(String shifted, String code) {

        char[] shift = shifted.toCharArray();

        char[] plain = code.toCharArray();

        int count = 0;

        for (int i = 0; i < shift.length; i++) {

            if (shift[i] == plain[i]) {

                count++;

            }

        }

        return count;

    }



    private void createBarChart(int[] count) {

        DefaultCategoryDataset data = new DefaultCategoryDataset();

        int maxValues = 30 > maxShift ? maxShift : 30;

        

        for (Integer i = 1; i <= maxValues; i++) {

            Integer category = 0;

            if (isPeak(count, maxValues, i)) {

                category = 1;

            }

            data.addValue(count[i], category, i);

        }

        

        JFreeChart chart = ChartFactory.createBarChart("Coincidence Count",

                "Shift", "Coincidences", data, PlotOrientation.VERTICAL, false,

                false, false);

        

        JFrame frame = new JFrame();

        frame.setVisible(true);

        frame.setSize(800, 600);

        frame.setLocationRelativeTo(null);

        frame.add(new ChartPanel(chart));

    }



    private boolean isPeak(int[] count, int maxValues, Integer i) {

        return i > 1 && (i + 1) <= maxValues && count[i - 1] < count[i] 

                && count[i + 1] < count[i];

    }

}