JAVA EXECUTABLE JAR PROBLEM

I have created many little programs in many class, but when I end I erase all the main class and start a new program, and always wanted to save the programs as executable so I can start another program without erasing the one I made.

I use eclipse, and always had try to export my program as a runnable jar, it does export it but I can run it, it said me a lot of things that I don't understand, there is an execption that I don't know how to fix it

MissingFieldException
at com.sun.javaws.jnl.XMLFormat.parse(Unknown Source)
at com.sun.javaws.jnl.LaunchDescFactory.buildDescriptor(Unknown Source)
at com.sun.javaws.jnl.LaunchDescFactory.buildDescriptor(Unknown Source)
at com.sun.javaws.jnl.LaunchDescFactory.buildDescriptor(Unknown Source)
at com.sun.javaws.Main.launchApp(Unknown Source)
at com.sun.javaws.Main.continueInSecureThread(Unknown Source)
at com.sun.javaws.Main$1.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

I have searching in google and still don't know what to do, they say me I need a manifest, but still no idea.

Thanks man, I though this help request will be ignored and forgotten.
I open it as rar, and I don't see nothing special, just that all the class that I have made are there even if the main class doesn't call them, and well I though that java erase all the inneficient classes once exported or even when you are programing.
Also I use eclipse and use his option of create jar, maybe I can do it manually but I don't understand the tutorials, I always stuck in the manifest text, after that I get lost and don't know what to do.

Would you mind if I send you somehow the 4 clases and 3 images? if you can do it with no problem I think there is something wrong with my computer I really don't have any idea of what is happening so can't help you to much in order to help me :( but this problem is getting my nerves.

I already download netbeans, I got the feeling that finally I will make it, but I found myself with somethings that I don't understand, do I have to create a manifest in netbeans? and also they said me that I have to put this: jar cf jar-file input-file(s)but I don't know where to put it.