JAVA第五次作业

老师，没有弄懂，就参考同学

import java.awt.Color;
import java.awt.BorderLayout;
import java.io.File;
import java.awt.Container;
import java.awt.event.ActionEvent;
import java.util.ArrayList;
import java.util.List;

import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;

public class FileUtils extends JFrame{
/**
* 列出指定文件夹（目录）中的所有文件或目录的名额
* @param dri File类型指定的文件夹（目录）
* @throws IllegalAccessException
*/
public static String listDirectory(File dir) throws IllegalAccessException{
if(!dir.exists()){
throw new IllegalAccessException("目录"+dir+"不存在");
}

//判断dir下关联的文件和目录是否存在
if(!dir.isDirectory()){
//如果不存在抛出异常
throw new IllegalAccessException(dir + "不是目录");
}
String[] fileName = dir.list();
String name ="";
for(String a : fileName){
name=name+a+"\n";}
return name;
}

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
// TODO Auto-generated method stub
JFrame frame=new JFrame();
JPanel main_panel =new JPanel(new BorderLayout());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//frame.setLayout(null);
String[] itme =new String[]{".jpg",".zip",".doc"};
JComboBox box=new JComboBox();
for(int i=0;i<itme.length;i++){
box.addItem(itme[i]);
}
box.setEnabled(true);
box.setEditable(true);
box.setMaximumRowCount(6);
box.setBounds(230,30,130,25);

frame.setBounds(400,300,400,200);
frame.setVisible(true);
JTextArea main_text =new JTextArea();
main_text.setBackground(Color.BLACK);
JScrollPane AA=new JScrollPane();
AA.setViewportView(main_text);
main_text.setEnabled(false);
main_panel.add(box,BorderLayout.NORTH);
main_panel.add(AA,BorderLayout.CENTER);
frame.add(main_panel);

try {
String str=FileUtils.listDirectory(new File("C:\\Users\\Administrator\\Desktop\\Java作业5\\soundPlayer\\audio"));
main_text.setText(str);
}
catch (IllegalAccessException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
frame.setBounds(300,400,300,400);
frame.setVisible(true);

}

}