java 中的class loader

The class loader concept, one of the cornerstones of the Java virtual machine, describes the behavior of converting a named class into the bits responsible for implementing that class. Because class loaders exist, the Java run time does not need to know anything about files and file systems when running Java programs.

What class loaders do

Classes are introduced into the Java environment when they are referenced by name in a class that is already running. There is a bit of magic that goes on to get the first class running (which is why you have to declare the main() method as static, taking a string array as an argument), but once that class is running, future attempts at loading classes are done by the class loader.

At its simplest, a class loader creates a flat name space of class bodies that are referenced by a string name. The method definition is: