An applet component that draws a bar chart : Applet « Swing JFC « Java

An applet component that draws a bar chart


<applet code="Chart.class" width=400 height=300>
<param name="title" value="Diameters of the Planets"/>
<param name="values" value="9"/>
<param name="name.1" value="Mercury"/>
<param name="name.2" value="Venus"/>
<param name="name.3" value="Earth"/>
<param name="name.4" value="Mars"/>
<param name="name.5" value="Jupiter"/>
<param name="name.6" value="Saturn"/>
<param name="name.7" value="Uranus"/>
<param name="name.8" value="Neptune"/>
<param name="name.9" value="Pluto"/>
<param name="value.1" value="3100"/>
<param name="value.2" value="7500"/>
<param name="value.3" value="8000"/>
<param name="value.4" value="4200"/>
<param name="value.5" value="88000"/>
<param name="value.6" value="71000"/>
<param name="value.7" value="32000"/>
<param name="value.8" value="30600"/>
<param name="value.9" value="1430"/>

   This program is a part of the companion code for Core Java 8th ed.

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <>.

import java.awt.*;
import java.awt.font.*;
import java.awt.geom.*;
import javax.swing.*;

 * @version 1.33 2007-06-12
 * @author Cay Horstmann
public class Chart extends JApplet
   public void init()
      EventQueue.invokeLater(new Runnable()
            public void run()
               String v = getParameter("values");
               if (v == null) return;
               int n = Integer.parseInt(v);
               double[] values = new double[n];
               String[] names = new String[n];
               for (int i = 0; i < n; i++)
                  values[i] = Double.parseDouble(getParameter("value." + (i + 1)));
                  names[i] = getParameter("name." + (i + 1));

               add(new ChartComponent(values, names, getParameter("title")));

 * A component that draws a bar chart.
class ChartComponent extends JComponent
    * Constructs a ChartComponent.
    * @param v the array of values for the chart
    * @param n the array of names for the values
    * @param t the title of the chart
   public ChartComponent(double[] v, String[] n, String t)
      values = v;
      names = n;
      title = t;

   public void paintComponent(Graphics g)
      Graphics2D g2 = (Graphics2D) g;

      // compute the minimum and maximum values
      if (values == null) return;
      double minValue = 0;
      double maxValue = 0;
      for (double v : values)
         if (minValue > v) minValue = v;
         if (maxValue < v) maxValue = v;
      if (maxValue == minValue) return;

      int panelWidth = getWidth();
      int panelHeight = getHeight();

      Font titleFont = new Font("SansSerif", Font.BOLD, 20);
      Font labelFont = new Font("SansSerif", Font.PLAIN, 10);

      // compute the extent of the title
      FontRenderContext context = g2.getFontRenderContext();
      Rectangle2D titleBounds = titleFont.getStringBounds(title, context);
      double titleWidth = titleBounds.getWidth();
      double top = titleBounds.getHeight();

      // draw the title
      double y = -titleBounds.getY(); // ascent
      double x = (panelWidth - titleWidth) / 2;
      g2.drawString(title, (float) x, (float) y);

      // compute the extent of the bar labels
      LineMetrics labelMetrics = labelFont.getLineMetrics("", context);
      double bottom = labelMetrics.getHeight();

      y = panelHeight - labelMetrics.getDescent();

      // get the scale factor and width for the bars
      double scale = (panelHeight - top - bottom) / (maxValue - minValue);
      int barWidth = panelWidth / values.length;

      // draw the bars
      for (int i = 0; i < values.length; i++)
         // get the coordinates of the bar rectangle
         double x1 = i * barWidth + 1;
         double y1 = top;
         double height = values[i] * scale;
         if (values[i] >= 0) y1 += (maxValue - values[i]) * scale;
            y1 += maxValue * scale;
            height = -height;

         // fill the bar and draw the bar outline
         Rectangle2D rect = new Rectangle2D.Double(x1, y1, barWidth - 2, height);

         // draw the centered label below the bar
         Rectangle2D labelBounds = labelFont.getStringBounds(names[i], context);

         double labelWidth = labelBounds.getWidth();
         x = x1 + (barWidth - labelWidth) / 2;
         g2.drawString(names[i], (float) x, (float) y);

   private double[] values;
   private String[] names;
   private String title;


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