Develop Reference

How to fix error while installing NetBeans?

I have installed Java and am trying to install NetBeans 11.3 on my Windows 10 but after I ran the exe. installer, an error message popped up:
An unexpected exception happened in thread main
java.lang.NoClassDefFoundError java/util/jar/Pack200

NetBeans have problems with the jdk-14, because I suppose that you have install the jdk-14 so uninstall it and try it with the jdk-13.0.2.

Sorry, but in my opinion is to install an old version from Java no solution, just because it works. When someone has problems with his Firewall, simply disable the Firewall would also be no solution.
https://www.java.com/en/download/faq/other_jreversions.xml
We highly recommend users remove all older versions of Java from your
system. Keeping old and unsupported versions of Java on your system
presents a serious security risk. Removing older versions of Java from
your system ensures that Java applications will run with the most
up-to-date security and performance improvements on your system.
The "real" solution would be a reprogramming of the NetBeans installer.
This used function was suggested for deprecated on 2018-04-04, which was done on 2018-08-23.
https://bugs.java.com/bugdatabase/view_bug.do?bug_id=8200752
The removal was suggested on 2019-10-08, which was done on 2019-12-18.
https://bugs.java.com/bugdatabase/view_bug.do?bug_id=JDK-8232022
https://bugs.java.com/bugdatabase/view_bug.do?bug_id=JDK-8232022
We assume that developers who rely on Pack200 have had enough notice about its proposed removal to make alternative arrangements. … We assume that developers who use pack200 to shrink application JARs can switch to either the jlink tool or the jpackage tool to create application-specific runtimes with an optimized form factor.
edit: I solved it this way.
uninstalled JDK 14
installed JDK 13.0.2
installed Apache NetBeans
installed JDK 14
open C:\Program Files\NetBeans\netbeans\etc\netbeans.conf and changed path to JDK
uninstalled JDK 13.0.2
Now NetBeans runs with the JDK 14.

Yes, I got it working as follows from cmd, when referring to older version:
Apache-NetBeans-11.3-bin-windows-x64.exe --javahome "C:\Program Files\Java\jdk-12.0.2"

The https://netbeans.apache.org/download/nb113/nb113.html site now has this
memo:
The installers will not run under JDK 14 because usage is made of the Pack200 Tools and API, for packing and unpacking, which is removed in JDK 14, see JEP 367.

If several JDK versions are installed, then you need to define the environment variable "JAVA_HOME" where to set the path to JDK-12.
Details are described here. (Only in Russian)

An alternate way to Andy's.
(Windows)
1) Right click on "Apache-NetBeans-11.3-bin-windows-x64" installer and select "Create shortcut".
2) Right click on the created shortcut and select "Properties".
3) In the "target" textbox, add your under 14 JDK version path at the end, here is how mine looks like:
C:\Users\userfoldername\Desktop\Apache-NetBeans-11.3-bin-windows-x64.exe --javahome "C:\Program Files\Java\jdk-13"
4) Press Ok when done, double-click on the shortcut and it should install fine now.

Switching to openJDK 12 worked for me too. But instead of uninstalling JDKs or manually changing the env, I use Sdkman.io which works like Node version manager if you have used that. It manages your JDKS for you and offers downloads of different versions (Open, Zulu, Graals) and will switch between them with with just a quick command.

I found a nice solution in 3 steps:
check all versions of the JDK path in Environment variables, if there is an outdated path please remove it and keep the latest version of the Java JDK bin path.
after the second step, please uninstall the Netbeans and re-install the latest version.
Netbeans will found the latest JDK path in case it was jdk14 and choose JDK latest version path for NetBeans.
solved

Just install JRE from oracle. Everthing will run fine. I have the same issue

Where to find required JRE files in OpenJDK for an JavaFX application to be wrapped using Launch4j

I'm building a GUI application in Java using JavaFX. So far I've been using Oracle JDK but due to licensing issues, I've decided to move on to OpenJDK or Azul Zulu. They don't come with JavaFX so I built OpenJFX myself on Ubuntu 16.04 (running on WSL).
Now, to wrap the application using Launch4j, I need the only the required JRE files to keep the application size minimum. In Oracle JDK distributions JRE is simply found in JRE folder, however, OpenJDK and OpenJFX have a different structure and I could not find (or missed, my bad) any documentation relevant to my question.
tl;dr: Need the location/path of minimum of required JRE files from OpenJDK and OpenJFX to wrap a cross-platform application using Lanuch4j.

Eclipse compiling with JRE or JDK

I have one question in my mind and I should note that I know the differences between JDK and JRE. I am not a new programmer in Java.
What I would like to ask is in Eclipse I can specify the compilation environment (correct me if I a wrong) in window> Preferences but we can also change it for a specific project.
OK. I added jre and jdk folder in the options. I can use both.
But JRE has no javac (no java compiler) in it. So how it is possible that some projects requires that I need to change to jre1.7 to COMPILE?
I was getting some minor.major version error and setting JRE solved my problem?
How can this be possible?
In fact now I realized something.
Ok the question changes a little.
I saw that these are VM not compiler. I understood.
Does JDK have also JRE in it? so if I specify JDK1.8 I am setting jre1.8 as VM and if I specify JRE1.7 I am setting jre1.7 as VM?
Is it right?
It makes confusions. Why JDK has JRE in it?

JDK has whole JRE (regular Java VM) inside, in order to allow you to run what you will develop with it.
Theoretically someone could make some small-JDK with just tools and without JRE, but it would make a whole lot more confusion as to which tools version run with which JVM version (most JDK tools needs JVM to be run). Look at you, how many people have only this problem? So it is bundled together, tools and JRE as a whole named JDK, thanks to that you have some guarantee that those JRE and tools will work together.
JRE - Java Runtime Environment - allows you to run java programs
JDK - Java Development Kit - allows you to run and develop java programs
JDK = JRE + tools for developer
Also note, that You can choose for the java compilation process two things:
compatibility with source version - this is basically the syntax you are allowed to use.
compatibility with VM version - this is the minimum VM level on which you can run the compiled binaries.
example from your post: If you have compiled something as Java 8, you can't run it on Java 7, this is the minor/major version problem you have. But the opposite (to run something for Java 7 on Java 8) is valid.
in your example JDK8 and JRE7 both are just fully functional VM's, but JDK8 has additionally (in comparison to JRE) development tools inside it.

Can I have two versions of the JDK on my computer?

I'm trying to set the IntelliJ IDEA JDK to version 1.8 (because it's the latest). When I navigate to System/Library/Frameworks/JavaVM.framework IntelliJ IDEA shows 1.6. When I type java -version it shows 1.8. I found that command under "Finding default JDK on OSX" https://www.java.com/en/download/help/version_manual.xml
I'm confused what versions of the JDK I have... and where they are located. Appreciate any help.

Yes, you can. You have JDK 1.6 and 1.8 installed on your computer. According to the Jetbrains website, all their products require Apple JDK 1.6 to be installed in order to run on Mac.
To make IntelliJ IDEA use JDK 1.8, you will need to edit /Applications/<Product>.app/Contents/Info.plist file and change JVMVersion from 1.6* to 1.8* :
<key>JVMVersion</key>
<string>1.8*</string>

To start off java will usually uninstall any version of the JDK when you get an update. Secondly if you want to check to see what version you are running I would go into what ever you are using to program and see what version you are compiling under (For example netbeans or eclipse). If it says 1.8 that is what you are running and same for 1.6. If this is really becoming a super big problem all you have to is uninstall java then re install and it should fix it.

You can have many different versions of Java on your system. In general Java depends on environment variables and the PATH environment variable. Some programs and tools look for tool specific environment variables to allow you to use a specific version of Java for that particular tool.
In the case of IntellJ the link that Eddie B posted in his comment explains how IntellJ determines which "installation" of Java it should use.

Upgrade Java version for Web Application

I have a web Application and i need to upgrade java jre version from 6 to 7 .I am using Eclipse as IDE.I tried to update the Jre from eclipse .I have even updated the JAVA_HOME environment variable but i am getting following error
C:\Program Files\Java\jdk1.7.0_55\jre..\lib\tools.jar
Please ensure you are using JDK 1.4 or above and
not a JRE (the com.sun.tools.javac.Main class is required).
In most cases you can change the location of your Java
installation by setting the JAVA_HOME environment variable.
Thanks

Download java hereand install it as a common application.
Then in Eclipse use Window->Prefrences->Java->Installed JREs

#Roman Bondar I guesss OP wanted to know more than just the setting.
Basically, JREs are meant to be downwards compatible, so that you are able to execute java classes compiled with version 6 with a runtime from java 7.
But as always, there may be special cases when things have to be changed, e.g. container or libraries. I remember a case back when I migrated to java 6 that it required a special version of JBoss.
Check out this Oracle blog as a starting point.