如何逐步绘制JTable单元？

Question

如何防止JTable擦除以前涂过的细胞？ （完整的SSCCE如下）

此表中的每个单元格以1％的概率随机改变颜色，每20毫秒调用JTable#repaint()。

以下是Cell组件的代码：

class MyCell extends JComponent {
    private Color color = null;
    private final Random rand = new Random();
    private final double probability = 0.01;  // change color with probability 1%
    @Override
    public void paintComponent(Graphics g){
        if (color == null || rand.nextDouble() < probability){
            color = new Color(rand.nextFloat(), rand.nextFloat(), rand.nextFloat());            
        }        
        g.setColor(color);
        g.fillRect(0, 0, getWidth(), getHeight());        
    }
}

颜色不会以99％的概率变化，所以我不需要重新绘制这样的细胞。我尝试以下实现（仅在颜色改变时绘画）：

class MyCell extends JComponent {
    private Color color = null;
    private final Random rand = new Random();
    private final double probability = 0.01;  // change color with probability 1%
    @Override
    public void paintComponent(Graphics g){
        if (color == null || rand.nextDouble() < probability){
            color = new Color(rand.nextFloat(), rand.nextFloat(), rand.nextFloat());
            g.setColor(color);
            g.fillRect(0, 0, getWidth(), getHeight());            
        }        
    }
}

结果如下：

• 请告知如何在部件决定的情况下有效地进行涂漆。我需要消除任何不必要的绘画并尽可能地降低CPU利用率。
• 另外，请告知，为什么这个小应用程序在普通PC上占用了大约10-15％的CPU。

这是完整的SSCCE：

    import java.awt.Color;
import java.awt.Component;
import java.awt.Graphics;
import java.util.Random;
import java.util.Timer;
import java.util.TimerTask;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JTable;
import javax.swing.SwingUtilities;
import javax.swing.table.DefaultTableModel;
import javax.swing.table.TableCellRenderer;

class MyCell extends JComponent {
    private Color color = null;
    private final Random rand = new Random();
    private final double probability = 0.01;  // change color with probability 1%
    @Override
    public void paintComponent(Graphics g){
        if (color == null || rand.nextDouble() < probability){
            color = new Color(rand.nextFloat(), rand.nextFloat(), rand.nextFloat());            
        }        
        g.setColor(color);
        g.fillRect(0, 0, getWidth(), getHeight());        
    }
}

class MyTableModel extends DefaultTableModel {
    final private int NROWS = 10;
    final private int NCOLS = 5;
    final private MyCell[][] cells = new MyCell[NROWS][NCOLS];

    public MyTableModel(){
        for (int i = 0; i < NROWS; i++){
            for (int j = 0; j < NCOLS; j++){
                cells[i][j] = new MyCell();
            }
        }
    }    
    public int getRowCount() {
        return NROWS;
    }
    @Override
    public int getColumnCount() {
        return NCOLS;
    }
    @Override
    public Object getValueAt(final int row, final int column) {
        return cells[row][column];
    }
    @Override
    public boolean isCellEditable(final int row, final int column) {
        return false;
    }    
}

public class JTableIncremental extends JTable {
    private final long period = 20; // repaint every [ms]
    JTableIncremental(){
        setModel(new MyTableModel());        
    }
    @Override
    public Component prepareRenderer(final TableCellRenderer renderer, final int row, final int column) {
        return (Component)dataModel.getValueAt(row, column);
    }    
    public void start(){
        new Timer().schedule(new TimerTask() {
            @Override
            public void run() {
                repaint();
            }
        }, 0, period);
    }

    public static void main( String[] args ) throws Throwable {
        final JFrame frame = new JFrame("Random colors table");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        final JTableIncremental table = new JTableIncremental();
        frame.add(table);
        frame.pack();
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                frame.setVisible(true);
                table.start();
            }
        });
    }    
}