import javax.swing.*;import java.awt.*;import java.io.File;public class ListFilesUI extends JFrame{    public static String listDirectory(File dir) throws IllegalAccessException{        if(!dir.exists()){            throw new IllegalAccessException("目录"+dir+"不存在");        }        if(!dir.isDirectory()){            //判断是不是目录            throw new IllegalArgumentException(dir+"不是目录");        }        String[] fileName = dir.list();            String name ="";        for(String a : fileName){            name=name+a+"\n";}        return name;        }        public static void main(String[] args) {        JFrame frame=new JFrame();        JPanel main_panel =new JPanel(new BorderLayout());        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);        //frame.setLayout(null);        String[] itme =new String[]{"all",".doc"};        JComboBox box=new JComboBox();        for(int i=0;i

结果截图：