有关滚动条的AdjustmentListener行为的问题

如何解决有关滚动条的AdjustmentListener行为的问题

我用Scrollbar示例修改了一个现有的JTable，并为此示例添加了一个Adjustment Listener和JMenu项。

执行示例并调整Frame的大小影响滚动条时，或者如果滚动条被移动，则按预期方式执行侦听器。访问工具栏上的菜单将触发调整侦听器。

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.AdjustmentEvent;
import java.awt.event.AdjustmentListener;

import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JScrollPane;
import javax.swing.JTable;

public class AdjustmentListener_Example3 
{
    static int x = 0;
    public static void main(String[] argv) 
    {
        JFrame frame = new JFrame();
        JTable table = new JTable(data,col);
        JScrollPane scrollPane = new JScrollPane(table);
        scrollPane.getVerticalScrollBar().addAdjustmentListener(new AdjustmentListener() 
        {
            @Override
            public void adjustmentValueChanged(AdjustmentEvent event) 
            {
                x++;
                System.out.println(x + " : " + event.getValue());
                String type = null;
                switch (event.getAdjustmentType()) 
                {
                    case AdjustmentEvent.TRACK:
                        type = "Track";
                        break;
                     
                    case AdjustmentEvent.BLOCK_DECREMENT:
                        type = "Block Decrement";
                        break;
                     
                    case AdjustmentEvent.BLOCK_INCREMENT:
                        type = "Block Increment";
                        break;
                     
                    case AdjustmentEvent.UNIT_DECREMENT:
                        type = "Unit Decrement";
                        break;
                     
                    case AdjustmentEvent.UNIT_INCREMENT:
                        type = "Unit Increment";
                        break;
                  }
                  System.out.println("    Type: " + type);

            }
        });
        frame.add(scrollPane);
        JMenuBar menuBar = new JMenuBar(); 
        JMenu menu = new JMenu("Menu"); 
        JMenuItem menuItem1 = new JMenuItem("Send Action To Scrollbar");
        menuItem1.addActionListener(new ActionListener() 
            {
                @Override
                public void actionPerformed(ActionEvent e) 
                {
                    AdjustmentListener[] adjustmentListeners = scrollPane.getVerticalScrollBar().getAdjustmentListeners();
                    adjustmentListeners[0].adjustmentValueChanged(new AdjustmentEvent(scrollPane.getVerticalScrollBar(),0));
                }
            });
        menu.add(menuItem1); 
        menuBar.add(menu); 
        frame.setJMenuBar(menuBar);         
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setBounds(20,20,500,500);
        frame.setVisible(true);
        
    }
    
    static String [][] data = {{"001","vinod","Bihar","India","Biology","65","First"},{"002","Raju","ABC","Kanada","Geography","58","second"},{"003","Aman","Delhi","computer","98","Dictontion"},{"004","Ranjan","Bangloor","chemestry","90",{"005",{"006",{"007",{"008",{"009",{"010",{"011",{"012",{"013",{"014",{"015",{"016",{"017",{"018",{"019",{"020",{"021",{"022",{"023",{"024",{"025",{"026",{"027",{"028",{"029",{"030",{"031",{"032","Dictontion"}};
    
    static String col[] = {"Roll","Name","State","country","Math","Marks","Grade"};
}

问题：

使用JButton，如果未创建任何侦听器，则什么也不会发生，但是即使在此示例中从未添加AdjustmentListener，滚动条也将起作用。这表明滚动条已经具有默认的侦听器来处理该功能。

调整侦听器是一种向滚动条添加其他侦听器，而不是覆盖现有侦听器的方法吗？

在移动滚动条时，Adjustment侦听器主要是执行其他非滚动条行为吗？

为什么在自定义侦听器中不需要@override注释以及对super的调用？