Versions of various software such as JDK, Eclipse, MyEclipse, Tomcat, and more (for you on version and compatibility issues)

In this article, we'll look at the version of JDK, Eclipse, MyEclipse, Tomcat, and so on.

A few concepts about the version
1.32-bit and 64-bit two versions:
In short, 64-bit operating systems support the identification of more than 4G of memory, and 32-bit not. So today we install most of the operating system and all kinds of software are 64-bit (because our computer is generally greater than or equal to 4G of memory). If you install a 32-bit JDK, but your jar package is compiled by a 64-bit JDK, it must not run. So, let's stress that you should install 64-bit for any programming related software, such as JDK or tomcat, so you don't have to be in trouble later. 64-bit how to identify? When the software is downloaded, it is generally noted that: Windows64bit or windows32bit. The downloaded installation package is also typically included in the name: *86 (32-bit), or *86_*64 (64-bit).
2. Install package and press pack two versions:
A lot of software, both the installation version, also has the decompression version. In Tomcat, for example, the installation version is all the way next. The decompression version is to unzip the package directly, even if it is completed.
We recommend the decompression version. First of all, the decompression version will not add to your registry or system services, and so on, you are not good at things, so that the unknown rubbish everywhere. Second, the decompression version can be removed at any time to re-unzip, you are very clear in your heart where it is. In summary, the decompression version is very controllable. And a lot of Java programming related software is installed in the form of decompression, decompression to a certain number of places under the configuration can be, very clean.
3. Release version of the version number:
In the case of JDK, JDK has 1.5 and jdk1.6 differences. No matter what the software, you usually take only one version to master when you study. If you are learning Java fundamentals with a 1.6 environment, you can search for "jdk1.6 new features relative to 1.5", "jdk1.7 new features" and so on. You will feel the same: I have already 1.6, and after reading 1.7 of the new features, equivalent to I will be 1.7. This way you will have a good version of the mind, there will be a clear version of the demarcation. You will not see the various versions of the burn, in fact, the version is the case. "Not just a few more features?" ”。
4. Relationship of other software and JDK:
You know, the JDK is the foundation of all Java software. In Tomcat, for example, it is software written in Java, meaning that its developers write code in the same Java language as you.
Developers use jdk1.6 to write tomcat6.0, and then use jdk1.6 to compile their own code and generate the jar package, then tomcat6.0 is the same version of jdk1.6.
Later released the jdk1.7, and someone wrote the TOMCAT7 with 1.7.
I think you should understand that you should try to match the software version, such as Tomcat6 run on the Jdk6, and then you write the software should be jdk6 compiled. This will greatly avoid errors. Of course, this is not an absolute requirement, since 1.7 is also java,1.6 java. The new version will be compatible with the older version. Sometimes, the lower version of the software can be run in a higher version of the environment, but we should try to avoid this, unless you control the version of the chest.

Ii. issues related to JDK
(1) Download
I don't teach you how to install the JDK, you can find a variety of tutorials online. I want to tell you how to make yourself aware of all aspects of the chest, are clear, not confused.
First, we go to the official website to download the genuine JDK. Search for "JDK", the first result is www.oracle.com English results. Click to go to the JDK download page. "The official website always hangs the latest version on the homepage and tells you what the latest and most stable version is, and will provide you with an old version of the download portal."
The page shows a download of 1.8, we do not download 1.8, we have to install 1.6. Pull the page to the end, find "Java Archive", in many Kaiyuan sites, can find the "Archive" link, it is "archive" means, that is, All historical documents exist here (and are organized neatly). Click on the link and you'll find JAVASE6.
There are many versions, both the operating system is divided into 64-bit and 32-bit, but also the "6u38" This small version of the difference, u38 is the 38th time to update the meaning, casually choose one can be, much the same. Remember to accept someone else's agreement, they let you register you also register it, not too lazy.
Solemn hint: Download JDK from the network disk or the software, it is shameful, like in the purchase of cattle tickets, and the software here is not as hard as the ticket sold by cattle, why do you want to steal this lazy? Downloading from other sources is not standard and unsafe.
In addition, download the JDK tutorial, also applies to any other software, I hope you can remember the method, develop habits. I will not repeat it later.
(2) Installation
First, clear a question. JDK can be installed at the same time, it is non-interference.
We clicked on the 1.6 installation package and removed the JRE when selecting the software component. The JRE is the Java Runtime Environment (Java Run Environment), which is the virtual machine that runs this version of the Java program. The JDK is the Java Development Kit (Java Development tool), a tool that compiles the Java files you write, along with the JRE. So in fact the extra JRE is superfluous, let's get rid of it.
In addition, there is an option for the JDK source code, which we reserve. It's not going to take much place, it might be used in the future.
If we install jdk1.6 in d/jdk/1.6, then the "1.6" folder is the Bin folder. Next, we can do the same with the jdk1.7 download installed in d/jdk/1.7.
So we have a lot of JDK installed. Next, configure the environment variables. What version of the default environment variable do you want to java_home set? Like 1.6.
java_home=d/jdk/1.6
In addition, according to the online steps, the configuration of classpath and path is possible. If you want to switch the default JDK, get rid of the javahome. What is the default JDK? If you download and unzip tomcat, you can click on the Startup.bat under its bin and sometimes it won't work. Why? Because you have a Java runtime environment, there is no default JDK configured. So, after configuring the default JDK, if the various Java software installed on your PC is not specially configured, it will run with the default JDK.

Third, the problem of Eclipse.
(1) Versions of Eclipse and JDK.
We know that eclipse is actually software developed in Java. Then there is the problem we have said before.
If you downloaded eclipse is jdk1.7 compiled, but you are jdk1.6 environment, certainly cannot run. How do I identify the JDK version of Eclipse?
I did not find the official website, but this blog introduction should be enough for you to use
http://blog.csdn.net/yuwenlanleng/article/details/59057450
If we install Eclipse, the JDK on the system cannot be too low.
(2) plugin version of Eclipse
Eclipse plug-ins are required to be compatible with eclipse. In other words, if our eclipse is compiled by a JDK of 1.6, then the plugin should be compiled by the JDK of 1.6. Otherwise, not on, or can not be used, can only change the plug-in version. If the plugin cannot be swapped, it can only be replaced by the JDK version of the plugin, for Eclipse.

How do I see the plugin version? Here, I'll paste the notes I made before.
————————————————————————————————————————————————————
Use 7zip or winrar to open the plugin's jar file and select any class file to copy it. Use the JDK's own anti-compilation command, JAVAP, to view the JDK version of compiling this class.
First copy the class to the JDK Bin directory and run the command line (both for convenience) in this directory.
For example:
D:\jdk\jdk1.7_64\bin>javap-verbose Activator.class
Classfile/d:/jdk/jdk1.7_64/bin/activator.class
Last modified 2014-12-13; Size 1349 bytes
MD5 Checksum EBC57CE573F622B89267B0E8A47D00B1
Compiled from "Activator.java"
public class Org.apache.hadoop.eclipse.Activator extends Org.eclipse.ui.plugin.AbstractUIPlugin
SourceFile: "Activator.java"
Minor version:0
Major version:51
Flags:acc_public, Acc_super

Here is the table of JDK version and version number
Hexadecimal decimal

JDK1.5 31 49

JDK1.6 32 50

JDK1.7 33 51

JDK8 34 52

I am here 51, so I know this plugin is compiled with 1.7. Then the eclipse that installs the plug-in must also need to be 1.7 compiled.
————————————————————————————————————————————————————

Another important issue is that when we download eclipse, we find that it has many versions. Have standard, have Java EE's.
To define a concept, Eclipse is the foundation and all other functions are plug-ins. In other words, if you are not good at installing plug-ins, you can download the specific version according to the various versions it offers. If you are good at configuring plug-ins, you can install a relatively simple version.
(3) version of the software that eclipse can develop.
We know that eclipse is dependent on the JDK version of the system in order to run, so we jdk1.6 eclipse will not be able to develop jdk1.7 applications?
Of course not! What version of Eclipse can be developed, and what version of himself it doesn't matter.
We can configure the default JDK version to be used when developing apps in Eclipse's windows>preference>java>installed JRE. This version can be arbitrary.
Also, on the project, we can right-click >properties>java compiler to set the compiled version of the JDK for this project. This is where the configuration of our project is compiled by what version of the JDK.
Our project should also refer to the compiled version of the JDK, right? Right-click the project >build path. That is, configure the build path, and then add the JRE Library of the version you need.

(4) MyEclipse
MyEclipse is a plugin for eclipse, and you may find it confusing. For example, there is a charger that sets up the iphone, I say it is a mobile phone accessories, you should understand it? Then you should understand why MyEclipse is a plugin for eclipse, even though it looks like a software, like Eclipse is its plugin.
The MyEclipse all come with a JDK, under the binary folder. Note that this version of the JDK is the version of the MyEclipse that was compiled, and also the JRE used by this myeclipse runtime (it does not use the system default JDK, but with its own). What version of the JDK the MyEclipse runs on is configurable and is configured to modify the Myeclipse.ini file. When you open it, you'll see how it's configured, and you can change the default JDK directory to yours.
Each version of the myeclipse corresponds to what version of the JDK, which can be viewed through the above methods.
Four, multi-version coexistence problems
We might be developing several versions of the project at the same time, so we're going to configure the 6.0 and 7.0 versions of Tomcat in Eclipse as well.
We may also use different versions of plugins at the same time, so we need to download different versions of Eclipse to use simultaneously. Eclipse is not a conflict. Note, however, that you are configuring a workspace because different versions of the workspace are not the same.
Someone might use the myeclipse. This is a fee software, how to let two version of the MyEclipse run at the same time, you need to study. There are solutions on the web.

Five, finally, we look back at the source of the problem
This problem we always put in the last, because the learning source is really difficult, is not very common.
When you download any open source software, should be handy to download its source code, and in your eclipse, the source link to the jar package, so that you develop, at any time click into the view source code. Eclipse's source configuration, do not repeat here, please search by yourself.


Today's article is here, the content is a bit long, a little complicated. Thank you for your patience in reading and hope to help you. Welcome to comment on comments and suggestions.

Versions of various software such as JDK, Eclipse, MyEclipse, Tomcat, and more (for you on version and compatibility issues)