请教一个关于JScrollPane的问题

Question

scrollpane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS)
这样的话，不管是否需要滚动条，就会出现滚动条了。以前不出现滚动条，是因为你没有添加viewport，所以没必要显示滚动条。

Answer 1

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;public class JScrollBar1 implements AdjustmentListener
{
    JScrollBar scrollBar1;
    JScrollBar scrollBar2;
    JPanel panel1;
    JLabel label2 = new JLabel("刻度：",JLabel.CENTER);
        
    public JScrollBar1()
    {
        JFrame f = new JFrame("JScrollBarDemo");
        Container contentPane = f.getContentPane();
        
        JLabel label1 = new JLabel(new ImageIcon(".\\icons\\flower.jpg"));
        panel1 = new JPanel();
        panel1.add(label1);
        scrollBar1 = new JScrollBar(JScrollBar.VERTICAL,10,10,0,100);
        scrollBar1.setUnitIncrement(1);
        scrollBar1.setBlockIncrement(10);
        scrollBar1.addAdjustmentListener(this);
        
        scrollBar2 = new JScrollBar();
        scrollBar2.setOrientation(JScrollBar.HORIZONTAL);
        scrollBar2.setValue(0);
        scrollBar2.setVisibleAmount(20);
        scrollBar2.setMinimum(10);
        scrollBar2.setMaximum(60);
        scrollBar2.setBlockIncrement(5);
        scrollBar2.addAdjustmentListener(this);
        
        contentPane.add(panel1,BorderLayout.CENTER);
        contentPane.add(scrollBar1,BorderLayout.EAST);
        contentPane.add(scrollBar2,BorderLayout.SOUTH);
        contentPane.add(label2,BorderLayout.NORTH);
        
        f.setSize(new Dimension(200,200));
        f.show();
        f.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                    System.exit(0);
            }
        });
    }
    
    public void adjustmentValueChanged(AdjustmentEvent e)
    {
        if ((JScrollBar)e.getSource() == scrollBar1)
            label2.setText("垂直刻度："+e.getValue());
        if ((JScrollBar)e.getSource() == scrollBar2)
            label2.setText("水平刻度："+e.getValue());
    }
    public static void main(String[] arg)
    {
        new JScrollBar1();
    }
}
        

Answer 2

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;public class Edge extends JFrame{
public JPanel pane=new JPanel();    
public Edge(){
super("Drawing");
setSize(500,400);
JScrollBar bar1=new JScrollBar();
JScrollBar bar2=new JScrollBar(JScrollBar.HORIZONTAL);
pane.setLayout(new BorderLayout());
pane.add(bar1,BorderLayout.EAST);
pane.add(bar2,BorderLayout.SOUTH);
          setContentPane(pane);
ExitWindow exit=new ExitWindow();
addWindowListener(exit);
}
public static void main(String[] args) {
Edge frame=new Edge();
frame.setVisible(true);
}
class ExitWindow extends WindowAdapter{
public void windowClosing(WindowEvent e){
System.exit(0);
}
}
}