import java.applet.* ;
import java.awt.* ;
import java.awt.event.* ;
/*
  <applet code="Kadai14" width=300 height=300>
  </applet>
*/

public class Kadai14 extends Applet implements MouseListener, MouseMotionListener{
  Point p, Oldp ;
  int ox = 0, oy = 0 ;
  int r = 30 ;
  boolean drg = false ;
  Image buffer ;
  Graphics bufferg ;

  public void init(){
    Dimension d = getSize() ;
    buffer = createImage( d.width, d.height ) ;
    addMouseListener( this ) ;
    addMouseMotionListener( this ) ;
  }

  public void mouseClicked( MouseEvent me ){
  }

  public void mouseEntered( MouseEvent me ){
  }

  public void mouseExited( MouseEvent me ){
  }
  
  public void mousePressed( MouseEvent me ){
    //マウスが押されたときの座標を取得
    Oldp = me.getPoint() ;
    if( Math.pow( (double)(Oldp.x-(ox+r/2)), 2.0 )
      +Math.pow( (double)(Oldp.y-(oy+r/2)), 2.0 )
      <= Math.pow( (double)r/2, 2.0 ) )
      drg = true;//円内で押されたらdrg=true
  }

  public void mouseReleased( MouseEvent me ){
    //マウスが離された時、マウスの移動で円が動かないようにdrg=false
    drg = false ;
  }
  
  public void mouseDragged( MouseEvent me ){
    //マウスが円内でドラッグされ、動いたとき、
    //円の位置をマウスの移動量だけ増やす
    if( drg ){
      p = me.getPoint() ;
      ox += p.x -Oldp.x ;
      oy += p.y -Oldp.y ;
      Oldp = p  ;
      repaint() ;
    }  
  }

  public void mouseMoved( MouseEvent me ){
  }

  public void update( Graphics g ){
    paint( g ) ;
  }

  public void paint( Graphics g ){
    if( bufferg == null )
      bufferg = buffer.getGraphics() ;

    Dimension d = getSize() ;
    bufferg.setColor( Color.white ) ;
    bufferg.fillRect( 0, 0, d.width, d.height ) ;
    bufferg.setColor( Color.black ) ;
    bufferg.fillOval( ox, oy, r, r ) ;

    g.drawImage( buffer, 0, 0, this ) ;
  }
}