Java语言:

import java.awt.*;
import java.io.*;
import java.awt.event.*;
public class IOtest extends Frame implements ActionListener{
       private Frame f;
     private TextArea ta;   //ta用于显示打开的内容
     private Button btn;
     private FileDialog fd;
     private File file1 = null;
     //构造函数开始
      public IOtest(){
           btn = new Button("打开");
           ta = new TextArea(5,50);
           btn.addActionListener(this);//给按钮添加事件监听器
             }
             //给按钮添加行为
      public void actionPerformed(ActionEvent e){
          if (e.getSource()==btn) { //单击打开按钮时   
                fd = new FileDialog(f,"Open",FileDialog.LOAD);
                fd.setVisible(true);   //创建并显示打开文件对话框
               
              //if ((fd.getDirectory()!=null) && (fd.getFile()!=null)) {
               
                try {   //以缓冲区方式读取文件内容
               
                  file1 = new File(fd.getDirectory(),fd.getFile());
                    FileReader fr = new FileReader(file1);
                    BufferedReader br = new BufferedReader(fr);
                    String aline;
                    while ((aline=br.readLine()) != null)//按行读取文本
                    ta.append(aline+"\r\n");
                    fr.close();
                    br.close();
                  }
               catch (IOException ioe){
               
                  System.out.println(ioe);
                }
              }
           //}
             
      }
                
     
     
      public static void main(String []args){
           IOtest iof = new IOtest();//创建并初始化IOtest对象iof
           iof.show();
      }
     
          public void show()
         {
            f = new Frame("读入文件测试");         //初始化对象f
            f.setSize(500,300);                //设置窗口f的大小
            //设置布局管理器为FlowLayout
           f.setLayout(new FlowLayout(FlowLayout.LEFT,30,20));
           f.add(btn);   
           f.add(ta);               
           //为窗口f添加WindowListener监听器
           f.addWindowListener(new WindowAdapter(){
                      public void windowClosing(WindowEvent evt){ //实现windowClosing方法
                        f.setVisible(false);         //设置窗口f不可见
                        f.dispose();            //释放窗口及其子组件的屏幕资源
                        System.exit(0);            //退出程序
                    }
                });
                f.setLocation(200,200);
        f.setVisible(true);                //设置窗口f可视
    }
}