Develop Reference

OpenJDK for production and LTS?

My understanding from "Do you have to pay to use Java?" of Java programming language Free
is that I can go for OpenJDK(version 11) build provided I don't need LTS as both OpenJDK and commercial version are identical in terms of features. If I need to purchase LTS(Long term support) either I have to purchase support for OpenJDK or upgrade to same version of "commercial Oracle JDK build". Is that correct ?
Another question is why I need LTS ?
I think if we don't take LTS then any we don't get any support/patch for defects( or security patch). Right ?

I wrote a blog article discussing that topic in early 2019.
First, as far as I know, the OpenJDK team does not offer any premium support.
Second, normally one goes to the LTS for longterm support, mainly security updates.
Third, Oracle will only hand over the code for the LTS version to the OpenJDK team and only after the LTS has reached its end of life. This means that the OpenJDK community has to keep up with changes on their own.
Now to the topic on the JDKs being identical. They both pass the JCK and thus can be used as drop-in replacement for each other. The implementations, however, may vary.
There is a host of JDK providers, all with different support plans. Fact of the matter is, there is no free lunch. If one wants support, one has to pay.
A remark on your post: Please limit yourself to one question per post

OpenJDK is a free and open-source implementation of the Java Platform. The implementation is licensed under the GNU General Public License. You are free to use at any environment. But you won't get any kind of support from the Oracle and you've to rely on open communities support, later can be best than the OEM support some times.
LTS is a product life cycle management policy in which a stable release of software is maintained for a longer period of time than the standard edition. You get security updates for some good number of years.
Do you have to pay to use Java?
Answer is yes, Iff you use Oracle JDK for business, commercial, or production purposes.
Answer is No, if you use OpenJDK irrespective purpose or environment.
PS: this is all about licensing and it can change over a period of time.

LTS is supported for 3 years and will receive updates until it expires. When you use openjdk you need not pay for support or patches. I always go with LTS like java 11.
The non-LTS version will have newer features but they are short lived like 6 months. They don’t receive updates for long rather it is expected to upgrade to next version. Security patches are available on same version or next version.
If you don’t have a special usecase then open jdk is more than enough

Is there any valid point upgrading Java 8 to Java 11?

I'm working in a company that has many projects in Java 8. Those projects are valued as old, and our team would like to upgrade the version. However, we need valid points in order to unlock the situation.
Those projects are using Spring and Hibernate (if it's ever useful).
What factual points could we give to our company to upgrade the versions, if any factual points there is ?
Examples of useful, valid points would be:
Security improvements
Performances improvements
New libraries or framework updates which could ease the development process
New possibilites/features with an upgraded Java Version
...
Possibly, backed up with documentation or links to useful resources.

old Java version will eventually stop getting new security fixes, which will make your software more vulnerable
using an old software stack will make it harder to find new developers willing to work on your software. Java 8 probably isn't too old for that yet, but in a few years that will be similar to finding "Java 1.4 developers" right now.
using an old software stack can severely limit your selection of useful third-party libraries and/or tools. A given library that you really need might require a more recent Java version or (possibly even worse) a library that you already use increases it's Java version requirement with a new major release (leaving you stuck with an old Java version and an old software version that might be missing important bug fixes).
There are several advantages from switching to newer Java versions, which are probably not the main reason to switch, but could be considered additional incentives:
newer JDK implementations might have better optimizations (in JIT and Garbage Collection mostly) that might help you get better performance from existing hardware (or reduce your cloud computing costs)
newer Java versions tend to have support for more modern technology, like the newest TLS versions and cryptographic algorithms which can help you data more secure, if you use them correctly.
new language features might improve your code style, which makes your developers happier, which means less churn which saves money on hiring new developers.

The reason to jump from 8 to 11 is the support of Oracle (or other implementation).
You can find the roadmap of Oracle here. For Java8 you are safe up to March 2022 for the premier support and extended support to December 2030. For Amazon Corretto they will provide free support and updates for version 8 to (at least) June 2026.
So the major reason to update your JVM version is support and updates. You still have time to update your version but you also have to wait for you 3rd party library to deliver compatibility with Java 11.
If you wonder why from 8 to 11 and not to 9 or 10, the reason is that 9 and 10 are not marked as LTS (Long Time Support) meaning that the different implementation won't provide any support and updates (or not for long) for those version when the next one is release.

Security updates for Oracle Java 8 are only provided via enterprise licenses and you could save that amount by using newer stable releases.
Apart from that, using newer versions also guarantee better integration with modern JVM tools, like up-to-date build tools.

How can I get Java 11 run-time environment working since there is no more JRE 11 for download?

Java 11 does not come with a JRE for download, unlike past Java versions. I got an error "no java run-time environment" when running some Java-based software. To fix the problem, I had to install Java 8 JRE.
How can I get my PC to run Java 11 JRE given that there is no more JRE 11 to download?
I am using Windows 10.

The Answer by Stephen C is correct, and important.
Oracle no longer intends for end-users to be installing a JRE or a JDK. Java Applets in a browser and Java Web Start app delivery are both being phased out, leaving the end-user with no need for a JRE. Java-based apps are expected to bundle their own Java implementation. The only folks consciously installing a JDK will be developers & server-side sysadmins.
Important:
Understand clearly the nature of the OpenJDK project, as explained in Wikipedia
Read this white paper by Oracle of 2018-03, Java Client Roadmap Update
Read the white paper Java Is Still Free, authored by key members of the Java community.
Learn about:
Java Platform Module System
jlink (JEP 282)
jpackage (JEP 343)
Desktop apps are now expected to bundle their own Java runtime. Those tools listed above can create a very small runtime custom-fit to your particular app.
Here is a flowchart diagram that may help you finding and deciding amongst the various vendors providing a Java 11 implementation.
And a table mapping possible motivations or considerations leading to suggested vendors of Java.
Compatibility concerns
In the Comments, an question was raised, concern over compatibility issues between releases by various vendors.
Firstly, know that the OpenJDK project includes a vast suite of tests known as the OpenJDK Community Technology Compatibility Kit (TCK). Vendors are free to self-declare whether their release has passed those tests. These claims are not verified, and rely on the honor system. On my diagram above, I have check-marked "TCK" on the couple vendors I know have self-declared: Oracle JDK by Oracle & Zulu by Azul Systems.
All the products listed in the blue barrel area of my chart above are built almost directly on the OpenJDK source code. So generally, you should see virtually identical compatibility.
There are two areas of concern you might consider: Technology differences, and schedule of updates/patches.
As for technology differences, vendors using the OpenJDK project can ship with either the HotSpot engine or the OpenJ9 engine. These will differ on performance (faster/slower startup versus overall speed, more/less memory), but their behavior in terms of complying with the Java specifications should be identical. They could differ, and certainly either might present a flaw (that likely would be soon fixed) that the other lacked. Personally, I would not be concerned by this, but I mention it for completeness.
Another technology difference is the different kind of JVM used by Zing by Azul Systems and GraalVM by Oracle. Either of these might differ in some way from each other or from the other products, because they intentionally have a different kind of JVM implementation, to offer special features. But given the thoroughness of the Java specs, they should not be incompatible. If they were, you can expect any compatibility problem to be rapidly resolved. If I needed the special features of either of these products, I would use them with full confidence.
Another possible concern is the speed with which a vendor might update their own releases with certain bug fixes or security patches. For example, Oracle has stated that they reserve the right to immediately ship any ready patches to their own customers, while submitting those to the OpenJDK project for consideration. Certainly, any of the vendors providing commercial support are likely to rush a fix or patch to their paying customers. Those releases built as a courtesy to the community provided free-of-cost may take longer to update, likely after the OpenJDK project has incorporated a fix/patch.
And each vendor is free to modify their code base at will, as long as they comply with the Java specs. For example, the Corretto team at Amazon has already made improvements to their own release, and then shared those changes upstream to the OpenJDK project. There may a gap in time before OpenJDK incorporated those changes, if they decide to do so. So it is possible that various releases might differ. But at this point, all of the vendors in the Java community seem to have sincere commitments to work together to prevent fragmentation. So, again, I have no real concern here, but mention this for completeness.

Right now, there seem to be no free + easy Oracle-supported Java 11 JRE (only) options. Your options are:
Download and use an OpenJDK Java 11 JDK from the OpenJDK site.
Download and use an Oracle Java 11 JDK from the Oracle site ... and be sure that you fully understand the restrictions on "commercial use" that now apply to the Oracle Java 11+ releases.
Try to roll your own Windows JRE for Windows from the OpenJDK sources; see Create jre from OpenJDK Windows. (I wouldn't recommend doing this. There are better alternatives.)
Look into using the new jlink tool to create a custom image (basically a cut-down JRE) for your application. This seems to be the option that Oracle want 3rd-party application developers to use.
Talk to Oracle sales about a Java support contract, and specifically ask about how to get a JRE build. (I don't know what the answer will be. If someone does try this, and they get a positive response, please comment!)
Use a 3rd-party Java JRE distribution.
The list of Java vendors changes over time, but as of now it includes AdoptOpenJDK, Amazon, Azul, BellSoft, IBM, jClarity, Red Hat and SAP. See also: Difference between OpenJDK and Adoptium/AdoptOpenJDK
Some of these vendors offer JRE distros. Check their download sites.
Since (nearly) all Java vendors base their products on the same standard OpenJDK codebase that is used for Oracle Java, there is no reason to be concerned about the stability of a 3rd party JRE. Some vendors offer (paid for) support.
(Or switch from Windows to Linux. I can install an OpenJDK Java 11 JRE-only package from the distro package manager on recent versions of Ubuntu, Fedora, ...)
For those people who think that Oracle Java 11 and OpenJDK Java 11 are the same, please read the following from the Oracle download site:
Important changes in Oracle JDK 11 License
With JDK 11 Oracle has updated the license terms on which we offer the Oracle JDK. The new Oracle Technology Network License Agreement for Oracle Java SE is substantially different from the licenses under which previous versions of the JDK were offered. Please review the new terms carefully before downloading and using this product.
Oracle also offers this software under the GPL License on jdk.java.net/11
Notice that Oracle are saying that the licenses for Oracle Java and OpenJDK Java are different. (Not withstanding that the two are built from essentially the same source code base.) Ignore this at your peril!

You can use the "adoptopenjdk" project website to download latest jre and JDK https://github.com/AdoptOpenJDK/openjdk-jdk11
find latest link here > https://adoptopenjdk.net/releases.html?variant=openjdk11&jvmVariant=hotspot
Edit:
Problem has been fixed
I have used their night builds to workaround the problem of missing JRE in JDK package
https://adoptopenjdk.net/nightly.html?variant=openjdk11

zulu still maintains the jre (11 - 16) and it is recommended by some vendors.
you can download it on their site: https://www.azul.com/downloads/zulu/

As java releases are coming faster do we need to migrate the old java code base to latest version?

Java releases are coming faster than expected do we need to migrate the code stuff which is old version to newer one to make it more performance based and upto date.

do we need to migrate the old java code base to latest version?
No.
Quite the opposite. You may decide to stick with deploying only the Long Term Support (LTS) (see Wikipedia) versions of Java. The promise: A version that will be actively supported for years with updates for critical bugs/issues but no new features or changes that might break existing deployments. The first such LTS version is scheduled for 2018-09, to be known as either Java 11 or 18.9 LTS (with year and month as release number).
Oracle has announced the changes in release cadences and support policies in late 2017 and again 2018-03. So it may take some more months until we know the exact nature of what releases are supported for how long by whom at what price.
In particular, you may want to avoid ever deploying Java 9 as it has had a brief life, with free-of-cost public updates from Oracle ending this month, 2018-03. By the way, Simon Ritter wrote about 109 New Features in JDK 10.
One of the core ideas behind the new regularly-scheduled “release train” plan is that hundreds of finished features were held up for years waiting on the Java 9 release. In a project as wide and diverse as the Java platform, it makes much more sense to ship whatever features are deemed ready every quarter or semester. If you find such features useful for your future deployments, you may choose to adopt that release. Or you choose to limit yourself to mere experimentation, while waiting for a future LTS version with those features.
more performance based
Future releases may or may not have improvements related to performance. And those improvements may or may not benefit your particular deployments. You will have to make a choice at that time about whether any of the particular improvements are worth migrating any of your particular deployments.
By the way, regarding performance, work is underway to make alternate garbage collector implementations easier to build and deploy. You may wish to keep your eye on developments there.
and upto date
As discussed above, “being up-to-date” is a choice you will have to make release-by-release. Making that choice will be easier as the list of changes to each release will be shorter and therefor easier to understand, digest, and test.
While Oracle and the community are committing to make each release fully qualified as stable and definitely not a “beta” disguised as an official release, change always brings some degree of risk. You may decide to stick with LTS versions to avoid the changes.
Early access
You can still access pre-release versions of Java. At this moment with Java 9 being the official release, Java 10 release candidate is available for trial. And JDK 11 has early access builds available.
Resources
See the official Oracle Java SE Support Roadmap. And be aware that Oracle has announced and confirmed that it is busily working to make their Oracle Java implementation virtually identical to OpenJDK, including contributing some of their add-on tools that are currently commercial products.
Also, you may want to consider alternate sources of implementation and support for Java. For example: Azul Systems with Zing & Zulu, IBM/Eclipse with OpenJ9, RedHat, and so on.

There is no need to do it, but the question is whether the rest of your code base is distributed in e.g. 1.8 compliant.
Having 1.8 is mostly a comfort for developers, keeping old code base is fine. But I've also been revisiting a few old classes dealing with e.g. Process creation and concurrency basic bricks and I'm very happy to have done so.
So do it where you clearly gain for doing it, iff. you think you can expect such recent JRE from your clients. If you already have recent JRE dependency, do some refactoring as code is reused and you revisit old APIs, if some new feature clearly kills your old solution, but not systematically is my advice.
Biggest issue with upping Java version is clients can't run newer versions, otherwise old code runs just fine on newer JRE.

When Java 6 will be dropped will my application continue to work?

I am a bit worried about something and no matter how much i searched i could not find something or i could not search properly.
I have an application that runs on java 6 SE. Oracle mentions in the website that they will drop the Java 6 SE Deployment in June 2017. So that leaves me with a question. Will my application still run after the Java 6 end or will it crash?
Deployment Technology for Java SE 6 will be available until Jun 2017
Mentioned here

Will my application still run after the Java 6 end or will it crash?
It will continue to run.
If a user downloads and installs a Java 6 JRE / JDK, your application will run as before.
If a user has Java 7, Java 8, Java 9 .... etcetera, your application will run on those platforms provided that it is properly written. Things that might cause it to break include:
dependencies on restricted "internal" classes that have been changed or removed in a later release,
incorrectly written multi-threaded code that breaks due to platform differences,
a tiny number of documented incompatibilities, and
dependencies on 3rd-party libraries that have not been ported.
However ....
You ought to take the time to port your application to run on the latest version of Java. This is probably just a matter of compiling the codebase on the newer / newest Java JDK, and then running all of your unit and system tests. (But if you have extensive dependencies on old libraries that are no longer being maintained, then you may have a problem ...)
If you don't do this, your application is liable to become problematic for users who won't or cannot install an out-of-date (and probably insecure!) version of Java on their systems.
This is even more important for applications that depend on web deployment and Java plugins for browsers.

Yes. No. Maybe.
If you continue to use old JVM nothing will changes. Except you won't get bugfixes and security patches.
If you migrate to new JVM then in theory all should be fine (Java declare backward compatibility), but sometimes problems may occur. That's why you need to test you application with new JVM before you go into production.

As mentioned by some of the others, yes your application will still work. It just means they will be done supporting it.

Oracle’s poor wording is ambiguous
To answer the specific part of your question, let's look at the text of the Oracle page, Oracle Java SE Support Roadmap (retrieved 2016-10).
Support of Deployment Technology
The web deployment technology, consisting of the Java Plugin and Web Start technologies, has a shorter support lifecycle. For all major releases of Java SE starting with Java SE 7, Oracle provides five (5) years of Premier Support for these technologies. Extended Support is not available for the deployment stack. See the Oracle Lifetime Support Policy for details.
Deployment Technology for Java SE 6 will be available until Jun 2017.
This says that for (a) the Java Plugin for Java applet and for (b) Java Web Start specifically you cannot purchase additional technical support from Oracle beyond 2017-06. Other Oracle extended support contracts running beyond that date do not include technical support for the Java SE 6 version of this pair of deployment technologies.
That last sentence is poorly worded. I believe we can assume it should have begun with “Technical support for”. I understand the cause for your Question here.
As others have said, Oracle has never time-bombed any Java technology product nor have they ever announced any plans for doing so.
Oracle support for the plugin and for applets is practically moot as various operating systems and web browsers in recent years have been limiting or ending their support for Java applets due to security vulnerabilities. Java Web Start remains a viable platform for distributing local Java apps, though I recommend such apps move to later versions of Java.