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What does the JVM do when a class file that has already been loaded is replaced?

Eventually I want the tool to be able to upgrade the component on the fly, i.e. a running program can replace a certain package and then all future use of those classes run off the latest one. It isn't going to be a straight forward switch since the JVM loads the class into memory then what ever is on disk is irrelevant. Below is a short proof:

javac -classpath . Test.java
java -classpath . Test

I/O Trace:

d
Old Version
a
Old Version
d
Old Version
d
Old Version

Switch over to the latest version of the component:

mv Component.java Component.java.old
rm Component.class
mv Component2.java Component.java
javac -classpath . Component.java

First compile package one:

javac v1/com/milesbarr/test/Test.java

I/O Trace:

a
Old Version
b
Old Version
d
Old Version
f
Old Version

Conclusion

Code Listings

import java.io.*;

public class Test {
    public static void main (String args[]) {
	Component c = new Component();

	while (true) {
	    BufferedReader console = new BufferedReader (new InputStreamReader(System.in));
	    
	    try {
		int chosen = console.read();
	    }
	    catch (IOException e) {
		e.printStackTrace();
	    }

	    c.print();
	}
    }
}

public class Component {
    public void print () {
	System.out.println("Old Version");
    }
}

public class Component {
    public void print () {
	System.out.println("New Version");
    }
}