Location of Java standard classes?

Hi everybody,

I'm new to lunbuntu 12.10 and to Java. I have installed
java-7-openjdk-i386 and wonder in which directory the
standard classes of Java are. Where for instance can I find
java.lang.System.class if such file exists?
Is there a directory java/lang/ or something?

I have a directory /usr/lib/jvm/java-7-openjdk-i386/ and
the command "whereis java" yields:

java: /usr/bin/java /usr/lib/java /usr/bin/X11/java
/usr/local/java /usr/share/java /usr/share/man/man1/java.1.gz

Thanks for answers,
Januss