Unable To Load Class File Into Oracle Using Loadjava

I'm trying to load a class file into Oracle using loadjava and I get the following error:

ORA-29552: verification warning: java.lang.UnsupportedClassVersionError: helloworld (Unsupported major.minor version 51.0)

Presumably this is related to an inconsistency between the jdk that I used to compile helloworld and the Oracle JVM? Or something like that?

My JAVA_HOME is C:Program Files (x86)Javajre7bin
My javac version used to compile the code is javac 1.7.0_15
java -version is "1.7.0_15"
When I do a find on java.exe in the oracle installation directory (I'm running 11.2) I get

J-PC:J >find -name java.exe
./product/11.2.0/dbhome_1/jdk/bin/java.exe
./product/11.2.0/dbhome_1/jdk/jre/bin/java.exe
./product/11.2.0/dbhome_1/jre/1.5.0/bin/java.exe

Finally, the jdbc jar is ojdbc6.jar

Btw the code is just the usual little tester:

import oracle.jdbc.driver.*;
public class helloworld {
    public static String hello()
    {
        return "Hello World";
    }
    public static String hello(String s)
 
[Code]...

How can I get this class file loaded?