And also for the flag '-ea' which stated that it allow all the assertions for all package and the system classes which do not have a class loader. I would like to know which system classes has class loader and which has not. Is there any information provided by Sun? As I search for it a few hrs but still get nothing.
From 5 Secure Class Loading
5.2 The Primordial Class Loader
Because each class is loaded by its class loader, and each class loader itself is a class and must be loaded by another class loader, we seem to have the obvious chicken-and-egg problem, i.e., where does the first class loader come from? There is a "primordial'' class loader that bootstraps the class loading process. The primordial class loader is generally written in a native language, such as C, and does not manifest itself within the Java context. The primordial class loader often loads classes from the local file system in a platform-dependent manner.
Some classes, such as those defined in the java.* package, are essential for the correct functioning of the Java Virtual Machine and runtime system. They are often referred to as base classes. Due to historical reasons, all such classes have a class loader that is a null. This null class loader is perhaps the only sign of the existence of a primordial class loader. In fact, it is easier to simply view the null class loader as the primordial class loader.
Given all classes in one Java application environment, we can easily form a class loading tree to reflect the class loading relationship. Each class that is not a class loader is a leaf node. Each class's parent node is its class loader, with the null class loader being the root class. Such a structure is a tree because there cannot be cycles -- a class loader cannot have loaded its own ancestor class loader.