题目:使用单例模式设计一个多文档窗口,要求在主窗体中某个内部子窗体只能实例化一次,即只能弹出一个相同的子窗体。
类图
package cn.factory5;
import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.JButton;
import javax.swing.JDesktopPane;
import javax.swing.JFrame;
import javax.swing.JInternalFrame;
import javax.swing.JTextArea;
public class JInternalFrameDemo extends JFrame implements ActionListener {
private static JInternalFrame1 internalFrame;
Container contentPane = this.getContentPane();
public JInternalFrameDemo(){
super("主窗体");
contentPane.setLayout(new BorderLayout());
JButton button = new JButton("创建一个子窗体");
button.addActionListener(this);
contentPane.ad