SINGLE_SELECTION与SINGLE_INTERVAL_SELECTION区别

Question

SINGLE_SELECTION允许一次选择一行。 SINGLE_INTERVAL_SELECTION允许选择相邻的一系列行。 MULTIPLE_INTERVAL_SELECTION也允许选择相邻的列，但是带有扩展功能。但是我发现两个SINGLE_SELECTION与SINGLE_INTERVAL_SELECTION都是只能选一行啊

Answer 1

SINGLE_INTERVAL_SELECTION 要按着Shift才能选中多个

Answer 2

为什么这个SINGLE_INTERVAL_SELECTION 要按着Shift也不能选中多个import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
public class My12 extends JFrame implements ListSelectionListener,ItemListener
{
    private JLabel jl1,jl2;
    private JList jlist;
    private JComboBox jcb;
    String[] countries={"United States","United Kingdom","China","Germany","France","Canada"};
    My12()
    {
        super("Exercise 11.14");
        //初始化组件
        jl1=new JLabel("Choose Selection Mode");
        jl2=new JLabel();
        
        jlist=new JList(countries);
        jcb=new JComboBox();
        
        jcb.addItem("Single_Selection");
        jcb.addItem("Single_Interval_Selection");
        jcb.addItem("Multiple_Interval_Selection");
        jcb.setSelectedIndex(2);
        //创建面板并组合到框架
        JPanel jp1=new JPanel();
        jp1.setLayout(new FlowLayout());
        jp1.add(jl1);
        jp1.add(jcb);
        getContentPane().setLayout(new BorderLayout());
        getContentPane().add(jp1,BorderLayout.NORTH);
        getContentPane().add(jlist,BorderLayout.CENTER);
        getContentPane().add(jl2,BorderLayout.SOUTH);
        //注册事件侦听器
        jcb.addItemListener(this);
        jlist.addListSelectionListener(this);
    }
    //事件处理函数
    public void itemStateChanged(ItemEvent e)
    {
        int i;
        for(i=0;i<3;i++)
        {
            if                (jcb.getSelectedItem()==jcb.getItemAt(i))
            {
                break;
            }
        }
        switch(i)
        {
            case 0:{jlist.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);break;}
            case 1:{jlist.setSelectionMode(ListSelectionModel.SINGLE_INTERVAL_SELECTION);break;}
            case 2:{jlist.setSelectionMode(ListSelectionModel.MULTIPLE_INTERVAL_SELECTION);break;}
            default:break;
        }
    }
    public void valueChanged(ListSelectionEvent e)
    {
        int[] index=jlist.getSelectedIndices();
        String out=new String();
        for(int i=0;i<index.length;i++)
        {            out+=countries[index[i]];
            
        }
        jl2.setText(out);
    }
    //main
    public static void main(String[] args)
    {
        My12 my12=new My12();
        my12.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        my12.pack();
        my12.setVisible(true);
    }
}