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JVM vs JRE vs Java Plug-In and Yahoo Chat!

Ali Web
Greenhorn

Joined: Mar 13, 2004
Posts: 3
Hi
I am a little confused as to what is required in the browser to run an applet.
Do I require JVM installed in my browser?
Do I require Java Plug-In installed in my browser?
Do I require JRE installed in my browser?
What is the difference between these three?
My second question is about the version of JDK to use while developing Java Applets. I am planning to make a Chat Application similar to Yahoo chat. For that I made a beta version using JDK 1.4.2 but now the problem is that most of the client browsers have old version installed for e.g. 1.1.4 by Microsoft or 1.2 by Sun.
In this case almost every user that uses my chat applet has to download the latest version from http://java.sun.com/getjava otherwise it the chat applet doesn't work on their browser. And I don't want this to happen because most of the time it takes ages to download and install the latest Java version on client browser. Yesterday on Pentimum 4 having 512 MB RAM and Windows 98 with 56K modem and it took almost 45 minutes to download and install which is unacceptable.
If you see the Yahoo chat http://chat.yahoo.com you will see that it is developed in such a way that it supports almost all the browserd without having to install the latest version. This is what I want to achieve and I am looking from your input as to how do I make sure that the client doesn't need to install the latest version (or atleast very few clients need to install latest version). Do I need to make this chat application in an old JDK version for e.g. 1.1.6?
Jason Huntz
Greenhorn

Joined: Mar 10, 2004
Posts: 7
The JVM stands for java virtual machine. You will need a JVM of some kind to run any java code. Internet Explorer for a little while longer at least has a default JVM built into it, but it is a very old JVM. If you write to that, most people will be able to use your applet for now but in the future newer versions of IE will not have this default JVM installed. Every Java Runtime Environment(JRE) has a JVM. The Java Plugin if they still even call it that would be installed at the same time as the JRE.
If I were you I'd write to java 1.2 or 1.3 because 1.4 is still pretty new(just write it in 1.4 and compile with -target option set to compile to 1.2) unless I had used code features that aren't available as of that version. Some people may still need to do the download but it shouldn't be as many. Many of the larger computer makers have newer JVM's installed on their computers now anyway(though probably no newer than 1.3). That is just my opinion though and you could try to use the old microsoft jvm if you wanted. That is probably what Yahoo does though that jvm is pretty much obsolete
Ali Web
Greenhorn

Joined: Mar 13, 2004
Posts: 3
hmmm... yes you are write that in the future new version of IE will have new version of JVM rather than the old MS JVM 1.1.4 but whatever the version is it will support the old version due to backward compatibility.
its like those having JVM 1.4 or later can run the applet compiled in Java 1.3 but those having MS JVM 1.1.4 (most of the old browser have MS JVM by default) will not be able to run it.
so to be on the safe side i will stick to the old version. after doing some work i found out that if you compile your code in Java 1.2 then those having MS JVM 1.1.4 will be able to run it. but your code should contain AWT components rather than SWING otherwise it won't work.
 
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