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I have created an executable jar developed on java version 8.Jar was opening on double click. But as the oracle apps support only Java 6, I had to install JRE6 but then after JRE6 installation, my executable jar is not opening.

I have set the JDK 8 bin path in Path environment variables. Please suggest a solution for this problem. Why is the jar not opening after two JAVA versions in the system?

JAR should open even if two versions 6 and 8 of java are installed in the system.

You are facing Backward Compatibility problem,backwards compatibility means that you can run Java 6 program on Java 8 runtime, not the other way around.

You can Run Lower configuration on Higher Configuration not Vice-Versa

There are several reasons for that:

1. Bytecode is versioned and JVM checks if it supports the version it
   finds in .class files.


2. Some language constructs cannot be expressed in previous versions of
   bytecode.


3. There are new classes and methods in newer JRE's which won't work
   with older ones.

If you really, really want (tip: you don't), you can force the compiler to treat the source as one version of Java and emit bytecode for another, using something like this:

javac -source 1.8 -target 1.6 MyClass.java

Source: A program made with Java 8 can be run on Java 7?

In the short term,

the answer is yes. Since both JDK files are downloaded as jar fils it will ok to download both jar files. The reason to not opening after two java versions is as @Elliott said: "in the system is Java 6 can't run Java 8 compiled code, you should be getting an error." That's exactly true but the problem is how to use multiple versions of JDK in a single machine.

Then we have to move on to long term,

The tricky thing is to manage these multiple JDKs and IDEs. It’s a piece of cake if I just use Eclipse for compiling my code because the IDE allows me to configure multiple versions of Java runtime. Unfortunately (or fortunately), I have to use the command line/shell to build my code. So, it is important that I have the right version of JDK present in the PATH and other related environment variables (such as JAVA_HOME).

Manually modifying the environment variables every time I want to switch between JDKs, isn’t a happy task. But, thanks to Windows Powershell, I’m able to write a script that can do the heavy lifting for me.

Basically, what you want to achieve is to set the PATH variable to add the Java bin folder and set the JAVA_HOME environment variable and then launch the correct Eclipse IDE. And, I want to do this with a single command. Let’s do it.

1. Open a Windows Powershell.


2. I prefer writing custom Windows scripts in my profile file so that it is available to run whenever I open the shell. To edit the profile, run this command: notepad.exe $profile - the $profile is a special variable that points to your profile file.


3. Write the below script in the profile file and save it.

function myIDE{ $env:Path = “C:vraajavajdk7bin;” $env:JAVA_HOME = “C:vraajavajdk7” C:vraaideeclipseeclipse set-location C:vraaworkspacemyproject play }

function officeIDE{

$env:Path  = "C:vraajavajdk6bin;"

$env:JAVA_HOME = "C:vraajavajdk6"

C:officeeclipseeclipse

}

4. Close and restart the Powershell.


5. Now you can issue the command myIDE which will set the proper PATH and environment variables and then launch the Eclipse IDE.

As you can see, there are two functions with different configurations. Just call the function name that you want to launch from the Powershell command line (myIDE).

If any issue please put a comment below!