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Share a small Java application: applet

Y2J

May 18, 2017 am 10:15 AM

Java Applets are small applications written in Java language. They can be directly embedded into web pages and can produce special effects.

After the applet is compiled, it will Generate .class files and embed the .class files in html web pages. As long as the user connects to a web page, the applet will be downloaded to the user's computer along with the web page and run

The inheritance relationship of the applet class is as follows:

java.lang.Object

## java.awt.Component

java.awt.Container

java.awt.Panel

## java.applet.Applet

The life cycle of applet

is as follows

##The four main methods of applet
public void init(): Called by the browser or appletviewer to tell the current applet that it has been loaded into the system. This method is always called before the start() method is called for the first time.

public void start(): Called by the browser or appletviewer to tell the current applet that it should start executing. This method is called after the init() method, and this method is called every time the web page accesses the applet

public void stop(): Called by the browser or appletviewer to tell the current applet that it should stop execution. This method is called when the Web page containing the current applet is replaced by another Web page. This method is also called before calling the destroy() method. Method

public void destroy(): Called by the browser or appletviewer to tell the current applet that it has been asked to return and that it should clear any resources assigned to it

Please see the following code

import java.awt.*;
import java.util.*;
public class cam1 extends java.applet.Applet
{
     String s;
     int inits=0,starts=0,stops=0;
     public void init()
     {
    	 inits++;
    	 showStatus("now init");
    	 System.out.println("now init");
    	 pause();
    	 showStatus("leave init");
    	 System.out.println("leave init");
    	 pause();
     }
     public void start()
     {
    	 starts++;
    	 showStatus("now start");
    	 System.out.println("now start");
    	 pause();
    	 showStatus("leave start");
    	 System.out.println("leave start");
    	 pause();
     }
     public void stop()
     {
    	 stops++;
    	 showStatus("now stop");
    	 System.out.println("now stop");
    	 pause();
    	 showStatus("leave stop");
    	 System.out.println("leave stop");
    	 pause();
     }
     public void paint(Graphics g)
     {
    	 s="inits: "+inits+"starts: "+starts+"stops: "+stops;
    	 g.drawString(s, 10, 10);
    	 System.out.println("now paint: "+s);
    	 pause();
     }
     public void pause()
     {
    	 Date d=new Date();
    	 long t=d.getTime();
    	 while(t+1000>d.getTime())
    	 {
    		 d=new Date();
    	 }
     }
}

The applet viewer is as follows

##eclipse The Console in is as follows

now init

leave init

now start

leave start

now paint: inits: 1starts: 1stops: 0

now paint: inits: 1starts: 1stops: 0 //Zoom (zoom in)

now paint: inits: 1starts: 1stops: 0 //Zoom (zoom out)

now stop //Restart

leave stop

now init

##leave init

now start

leave start

now paint: inits: 2starts: 2stops: 1

now stop

leave stop

Embed it in html

<HTML>
<HEAD>
<TITLE>WELCOME </TITLE>
</HEAD>
<BODY> test
<APPLET code="cam1.class" WIDTH=750 HEIGHT=325>
</APPLET>
</BODY>
</HTML>

I am using Google Chrome and the web page opens as follows

## View the output of #System.out.println in the java console

Before setting the java console to display in the java control panel

When the window is resized, moved, or its contents change, paintFunction

Redraw the applet window

The console displays as follows

Java 插件10.13.2.20
使用 JRE 版本 1.7.0_13-b20 Java HotSpot(TM) Client VM
用户主目录 = C:\Users\Administrator
----------------------------------------------------
c:   清除控制台窗口
f:   终结在结束队列上的对象
g:   垃圾收集
h:   显示此帮助消息
l:   转储类加载器列表
m:   打印内存使用情况
o:   触发日志记录
q:   隐藏控制台
r:   重新加载策略配置
s:   转储系统和部署属性
t:   转储线程列表
v:   转储线程堆栈
x:   清除类加载器高速缓存
0-5: 设置跟踪级别为<n>
----------------------------------------------------
now init
leave init
now start
now paint: inits: 1starts: 1stops: 0
leave start
now paint: inits: 1starts: 1stops: 0   //缩放
now paint: inits: 1starts: 1stops: 0
now paint: inits: 1starts: 1stops: 0
now paint: inits: 1starts: 1stops: 0
now stop  //刷新网页
leave stop
Exception in thread "thread applet-cam1.class-1" java.lang.NullPointerException
	at java.awt.EventQueue.isDispatchThread(Unknown Source)
	at com.sun.deploy.uitoolkit.impl.awt.AWTAppletAdapter.runOnEDT(Unknown Source)
	at com.sun.deploy.uitoolkit.impl.awt.AWTAppletAdapter.doClearAppletArea(Unknown Source)
	at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)
	at java.lang.Thread.run(Unknown Source)
now init
leave init
now start
now paint: inits: 1starts: 1stops: 0
leave start

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