Instantiate class from jar file

Question

Need a quick hand...little bit of a rush here.
How do I go about instantiating a class from a jar file?
If my jar file resides at c:/MyApp/MyJar.jar
The contents of the jar file are:
meta-inf/MANIFEST.MF
A.java
How do I go about creating an instance of A? I see people saying to use the URLClassLoader, but I can't find any good sample code to clarify how it's done. Assuming I already know the name of the class I'm instantiating, could someone show me how the URLClassLoader is used please? Also, please note that the jar file is NOT in my classpath, and I am not able to put it there....because it needs to be dynamically loaded as a plugin. I'm not sure if that matters or not with regards to the instantiation.

Answer 1

Thanks so much for that..I think it's just about what I need. However, I'm still running into a bit of a snag. After executing the code and trying to run a method to print something out from the object I just loaded, it instead prints a memory location. So I don't think it is quite working as intended. Here's the code I'm working with at the moment....
String jarPath = baseDir + "myApp/plugins/" + fileName;
Manifest mf = jar.getManifest();
Attributes att = mf.getMainAttributes();
String className = att.getValue("Main-Class");
//System.out.println(className);
File file = new File(jarPath);
URL[] urls = new URL[] {file.toURL()};
ClassLoader loader = URLClassLoader.newInstance(urls);
Class dynmicallyLoadedClass = Class.forName(className, true, loader);
PlugIn plugin = (PlugIn) dynmicallyLoadedClass.newInstance();
System.out.println(plugin.toString());  //This prints out "TMGImporter@1ce50a9" instead of what it's supposed to....Also, I am using Java 1.4.2_08 so I can't use generics. There are no error messages, just the wrong output. The jar this is using actually contains two files, besides the manifest. The TMGImporter (which Im trying to instantiate) and a TMGImporter$1 anonymous inner class. There is no package declaration on the class.
Any thoughts?