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"/>
</applet>
/*
This program is a part of the companion code for Core Java 8th ed.
(http://horstmann.com/corejava)
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
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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 <http://www.gnu.org/licenses/>.
*/
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.setFont(titleFont);
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();
g2.setFont(labelFont);
// 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;
else
{
y1 += maxValue * scale;
height = -height;
}
// fill the bar and draw the bar outline
Rectangle2D rect = new Rectangle2D.Double(x1, y1, barWidth - 2, height);
g2.setPaint(Color.RED);
g2.fill(rect);
g2.setPaint(Color.BLACK);
g2.draw(rect);
// 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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