java.awt.Graphics - Where are abstract methods implemented?

In Class java.awt.Graphics, methods such as drawRect are abstract and have no implementation. So where are the implementations?. The code listed below works, but I cannot see how.   It is from the book Java How to Program (Deitel).

public class DrawArcs
{
   // execute application
   public static void main( String args[] )
   {
      // create frame for ArcsJPanel
      JFrame frame = new JFrame( "Drawing Arcs" );
      frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );

      ArcsJPanel arcsJPanel = new ArcsJPanel(); // create ArcsJPanel
      frame.add( arcsJPanel ); // add arcsJPanel to frame
      frame.setSize( 300, 210 ); // set frame size
      frame.setVisible( true ); // display frame
   } // end main
} // end class DrawArcs

// Fig. 12.24: ArcsJPanel.java
// Drawing arcs.
import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JPanel;

public class ArcsJPanel extends JPanel
{
   // draw rectangles and arcs
   public void paintComponent( Graphics g )
   {
      super.paintComponent( g ); // call superclass's paintComponent

      // start at 0 and sweep 360 degrees
      g.setColor( Color.RED );
      g.drawRect( 15, 35, 80, 80 );
      g.setColor( Color.BLACK );
      g.drawArc( 15, 35, 80, 80, 0, 360 );

      // start at 0 and sweep 110 degrees
      g.setColor( Color.RED );
      g.drawRect( 100, 35, 80, 80 );
      g.setColor( Color.BLACK );
      g.drawArc( 100, 35, 80, 80, 0, 110 );

      // start at 0 and sweep -270 degrees
      g.setColor( Color.RED );
      g.drawRect( 185, 35, 80, 80 );
      g.setColor( Color.BLACK );
      g.drawArc( 185, 35, 80, 80, 0, -270 );

      // start at 0 and sweep 360 degrees
      g.fillArc( 15, 120, 80, 40, 0, 360 );

      // start at 270 and sweep -90 degrees
      g.fillArc( 100, 120, 80, 40, 270, -90 );
                 
      // start at 0 and sweep -270 degrees
      g.fillArc( 185, 120, 80, 40, 0, -270 );
   } // end method paintComponent
} // end class ArcsJPanel