JAVA: Class Loading Hierarchy

The class loading hierarchy in Java is 

bootstrap class loader ---> extensions class loader -----> system class loader
1)bootstrap class loader
The bootstrap class loader loads the core Java libraries[5] 
(<JAVA_HOME>/lib directory). This class loader, which is part of the core JVM, 
is written in native code.

2)extensions class loader
The extensions class loader loads the code in the extensions directories 
(<JAVA_HOME>/lib/ext or any other directory specified by the java.ext.dirs 
system property). It is implemented by the sun.misc.Launcher$ExtClassLoader class.

3)system class loader
The system class loader loads code found on java.class.path, 
which maps to the system CLASSPATH variable. This is implemented 
by the sun.misc.Launcher$AppClassLoader class.