【例 11-19】一个滚动条与显示窗口同步变化的应用程序。窗口有一个方块，用鼠标拖运方块，或用鼠标点击窗口，方块改变显示位置，相应水平和垂直滚动条的滑块也会改变它们在滚动条中的位置。反之，移动滚动条的滑块，方块在窗口中的显示位置也会改变。
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
class MyWindow extends JFrame{
    public MyWindow(String s){
        super(s);
        Container con = this.getContentPane();
        con.setLayout(new BorderLayout());
        this.setLocation(100,100);
        JScrollBar xAxis = new JScrollBar(JScrollBar.HORIZONTAL,50,1,0,100);
        jScrollBar yAxis = new jScrollBar(JScrollBar.VERTICAL,50,1,0,100);
        MyListener listener = new MyListener(xAxis,yAxis,238,118);
        Jpanel scrolledCanvas = new JPanel();
        scrolledCanvas.setLayout(new BorderLayout());
        scrolledCanvas.add(listener,BorderLayout.CENTER);
        scrolledCanvas.add(xAix,BorderLayout.SOUTH);
        scrolledCanvas.add(yAix,BorderLayout.EAST);
        con.add(scrolledCanvas,BorderLayout.NORTH);
        this.setVisible(true);
        this.pack();
    }
    public Dimension getPreferredSize(){
        return new Dimension(500,300);
    }
}
class MyListener extends JComponent implements MouseListener, MouseMotionListener,AdjustmentListener{
    private int x,y;
    private JScrollBar xScrollBar;
    private JScrollBar yScrollBar;
    private void updateScrollBars(int x,int y){
        int d;
        d = (int)(((float)x/(float)getSize().width)*100.0);
        xScrollBar.setValue(d);
        d = (int)(((float)y/(float)getSize().height)*100.0);
        yScrollBar.setValue(d);
    }
    public MyListener(JScrollBar xaxis,JScrollBar yaxis,int x0,int y0){
        xScrollBar =xaxis;
        yScrollBar =yaxis;
        x = x0;
        y=y0;
        xScrollBar.addAdjustmentListener(this);
        yScrollBar.addAdjustmentListener(this);
        this.addMouseListener(this);
        this.addMouseMotionListener(this);
    }
    public void paint(Graphics g){
        g.setColor(getBackground());
        Dimension size = getSize();
        g.fillRect(0,0,size.width,size.height);
        g.setColor(Color.blue);
        g.fillRect(x,y,50,50);
    }
    public void mouseEntered(MouseEvent e){}
    public void mouseExited(MouseEvent e){}
    public void mouseClicked(MouseEvent e){}
    public void mouseRelease(MouseEvent e){}
    public void mouseMoved(MouseEvent e){}
    public void mousePressed(MouseEvent e){
        x = e.getX();
        y = e.getY();
        updateScrollBars(x,y);
        repaint();
    }
    public void mouseDragged(MouseEvent e){
        x = e.getX();
        y = e.getY();
        updateScrollBars(x,y);
        repaint();
    }
    public void adjustmentValueChanged(AdjustmentEvent e){
        if(e.getSource()==xScrollBar)
            x=(int)((float)(xScrollBar.getValue()/100.0)*getSize().width);
        else if(e.getSource()==yScrollBar)
            y = (int)((float)(yScrollBar.getValue()/100.0)*getSize().height);
        repaint();
    }
}
public class Example6_9{
    public static void main(){
        MyWindow myWindow = new MyWindow("滚动条示意程序");
    }
}