web development helpdesk

For any serious charting we use JFreeChart but for simple cases such as when we are mentoring Java students who need charting for their assignments we use Swing directly to paint the chart.

Here is a simple example of how a bar chart can be implemented using Swing.

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.util.LinkedHashMap;
import java.util.Map;

import javax.swing.JFrame;
import javax.swing.JPanel;


public class BarChart extends JPanel
{
	private Map<Color, Integer> bars =
            new LinkedHashMap<Color, Integer>();
	
	/**
	 * Add new bar to chart
	 * @param color color to display bar
	 * @param value size of bar
	 */
	public void addBar(Color color, int value)
	{
		bars.put(color, value);
		repaint();
	}
	
	@Override
	protected void paintComponent(Graphics g)
	{
		// determine longest bar
		
		int max = Integer.MIN_VALUE;
		for (Integer value : bars.values())
		{
			max = Math.max(max, value);
		}
		
		// paint bars
		
		int width = (getWidth() / bars.size()) - 2;
		int x = 1;
		for (Color color : bars.keySet())
		{
			int value = bars.get(color);
			int height = (int) 
                            ((getHeight()-5) * ((double)value / max));
			g.setColor(color);
			g.fillRect(x, getHeight() - height, width, height);
			g.setColor(Color.black);
			g.drawRect(x, getHeight() - height, width, height);
			x += (width + 2);
		}
	}

	@Override
	public Dimension getPreferredSize() {
		return new Dimension(bars.size() * 10 + 2, 50);
	}

	public static void main(String[] args)
	{
		JFrame frame = new JFrame("Bar Chart");
		BarChart chart = new BarChart();
		chart.addBar(Color.red, 100);
		chart.addBar(Color.green, 8);
		chart.addBar(Color.blue, 54);
		chart.addBar(Color.black, 23);		
		frame.getContentPane().add(chart);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.pack();
		frame.setVisible(true);
	}
}

written by objects \\ tags: bar chart, charting, custom painting, JFreeChart