CLASSPATH for System Classes

Hi,
I have a basic question about CLASSPATH. I read and understood that when I write my own Java files I need to set CLASSPATH Environment variable in order to locate the specific file by the JAVA Class Loader. But my question is that I have a JAVA file in which I am importing

Statement# 1Import java.util.*;
Statement# 2 Import myOwnPackage.*;

// Have some Source

When I want to compile this File I need to set the Class Path for the statement#2 to tell the class loader where the Package and where the Class File. This can be done in the System Environmental variable or at compile time by -CLASSPATH option. Up to here I am very well understood. When I compile this Java Source file by giving Class path for the Statement#2 (With out giving the class path for java.util ) I am able to compile and run successfully. But my question is that why I am not required to give or set the CLASSPATH for java.util ? Is this because this is system class ? Even if it is system class how can Class Loader is able to locate this ?
In my system I do not have any CLASSPATH for the java.util. I have Installed the JAVA in C:\Program Files\Java\j2sdk1.4.2_03.

I know this is a basic question but I am not able to understand this. I appreciate for the reply on this.

Moving to Java in General (Beginner)

The JVM internally maintains a location to the system classes; thus, you do not have to specify them in the classpath. (In older versions of Java, you did have to; however, this produced problems when running with the -cp version, so they essentially "hard linked" those classes.) The default ClassLoader knows how to load those classes by default, so you don't have to do anything.

Thanks for the clarification.