import java.awt.*;
import javax.swing.*;
import java.awt.event.*;

public class MyJFrame extends JFrame implements ActionListener
{
  JButton cmdExit=null;
  JPanel  panel=null;
  Container cPanel=null;

  public MyJFrame(String strTitle)
  {
    this.setTitle(strTitle);
    this.setAlwaysOnTop(true);
    this.setSize(400,300);
    this.setDefaultCloseOperation(this.EXIT_ON_CLOSE);
    init();
   }
 public void init()
 {
  cPanel=this.getContentPane();
  cmdExit=new JButton("关闭");
  cmdExit.addActionListener(this);
  panel=new JPanel();
  panel.add(cmdExit);
  cPanel.add(panel,BorderLayout.NORTH);
 }

 public void actionPerformed(ActionEvent ae)
 {
   if(ae.getSource()==cmdExit)
     {
      this.dispose();
     }
 }
}
调试后 总是出现
-------------------配置: <默认>--------------------
E:\JAVA\text\lch\MyJFrame.java:14: cannot resolve symbol
symbol  : method setAlwaysOnTop (boolean)
location: class MyJFrame
    this.setAlwaysOnTop(true);
    ^
1 error

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;

public class MyJFrame extends JFrame implements ActionListener
{
  JButton cmdExit=null;
  JPanel  panel=null;
  Container cPanel=null;

  public MyJFrame(String strTitle)
  {
    this.setTitle(strTitle);
    this.setAlwaysOnTop(true);
    this.setSize(400,300);
    this.setDefaultCloseOperation(this.EXIT_ON_CLOSE);
    init();
    //this.pack();
    this.show(true);
   }
public void init()
{
  cPanel=this.getContentPane();
  cmdExit=new JButton("关闭");
  cmdExit.addActionListener(this);
  panel=new JPanel();
  panel.add(cmdExit);
  cPanel.add(panel,BorderLayout.NORTH);
}

public void actionPerformed(ActionEvent ae)
{
   if(ae.getSource()==cmdExit)
     {
      this.dispose();
     }
}
public static void main(String[] args)
{
    MyJFrame f=new MyJFrame("demo");
    
}
}