How to make an application to work with any Java versions? - eclipse

Question

I have created a Java project application in eclipse and i am using the JRE System Library[JavaSE-1.7].
when i make an executable jar file of the application then test it on different computers which have different Java versions. The problem is that the jar file only works on some of the computers because of the java version.
my question is: is there away to make the application to check the computer see which java version it has and just use that version instead of the java version that was used to implement the project? in other words can you make an application which is not java version dependent?
any suggestion is of great help.
thanks
Thanks for all the suggestions and comments. But i think i'll just stick with the java 7 version and let the user know that they need java 7 to run it.

Answer 1

No, there's no way to check that, not in the way I think you mean.
In fact, on the one hand you have the Java version in which you compile the class (which you can choose), and on the other hand the Java version (of the JVM) in which your application runs (which you cannot choose).
Well, I do believe there's a way to check the Java version through some method call or similar, but I don't think it would help you here, I mean that I guess you can't do something like:
if(java-7) {
//do try-with-resources
} else {
// do usual try-statement
}
As #skiwi suggested, make sure your application compiles against an older Java version, and you should be fine with JVMs of that version and beyond.
I'm not sure what's causing your ClassNotFound error, but it could be that the JVM checks the required Java version needed and stops if it is above the available.
If you compile from the command line, there are switches to tell javac the source Java version and the target Java versions. I never had used them, so you better search for questions about them (i.e. javac source and target options). With those tools it will be the compiler that warns you against problems, without you having to explicitly check the version in your code.

Answer 2

There is a way to check the Java version, but you would need multiple executables to do it.
You would need a root executable, that would have a low-bar minimum Java version, simply so it can check the version of the systems, then it would launch an executable from there based on the system's Java version.
How you would come about this:
System.getProperty() allows you to, well, get system properties, along with a few other things, like versions of installed applications like Java.
You should create a separate JAR with one class:
public class Launcher {
public static void main(String[] args) {
String javaVersion = System.getProperty("java.version");
// Conditional to launch Jar file
if(correctVersion) { // if version is confirmed
Runtime.getRuntime().exec("java -jar whatever.jar");
}
}
}
The reason we need a root, lower bar executable, is because if the original executable can't run in the first place, how is it going to check the Java version?
Hope this works out for you. Sorry it took so long to get an answer.