swing窗口事件（WindowLIstener）监听器

一个窗体的所有变化，窗口的打开、关闭等都可以使用这个WindowListener接口进行监听

windowOpened(WindowEvent e)  窗体被打开

windowClosing(WindowEvent e) 窗体关闭

windowIconified(WindowEvent e) 窗体最小化

windowDeiconified(WindowEvent e) 窗体从最小化恢复

windowActivated(WindowEvent e) 窗体被选中

windowDeactivated(WindowEvent e) 取消窗体被选中

演示完整代码如下：

import java.awt.Color;

import javax.swing.JFrame;

import javax.swing.JScrollPane;

import javax.swing.JTextArea;

import java.awt.Dimension;

import java.awt.Point;

import java.awt.event.WindowEvent;

import java.awt.event.WindowListener;

public class DemoWindowEvent {

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