Classloader purpose

Question

What exactly is the purpose of a classloader and how exactly does it work.

Answer 1

What exactly is the purpose of a classloader and how
exactly does it work.jverd has pointed out some good links but just in case
you want a summary, Lets start from the building
blocks. The smallest unit of execution that gets
loaded by a ClassLoader is the Java class file. A
class file contains the binary representation of a
Java class, which has the executable bytecodes and
references to other classes used by that class,
including references to classes in the Java API.
Stated simply, a ClassLoader locates the bytecodes for
a Java class that needs to be loaded, reads the
bytecodes, and creates an instance of the
java.lang.Class class. This makes the class available
to the JVM for execution. Initially when a JVM starts
up, nothing is loaded into it. The class file of the
program being executed is loaded first and then other
classes and interfaces are loaded as they get
referenced in the bytecode being executed. The JVM
thus exhibits lazy loading, i.e., loading classes only
when required, so at start-up the JVM doesn't need to
know the classes that would get loaded during runtime.
Multiple instances of ClassLoaders exist in the Java 2
runtime, each loading classes from different code
repositories. For instance, Java core API classes are
loaded by the bootstrap (or primordial) ClassLoader.
Application-specific classes are loaded by the system
(or application) ClassLoader. In addition, an
application can define its own ClassLoaders to load
code from custom repositories e.g the web server
classloaders. Java 2 defines a parent-child
relationship between ClassLoaders. Each ClassLoader
except the bootstrap ClassLoader has a parent
ClassLoader, conceptually forming a treelike structure
of ClassLoaders. The bootstrap ClassLoader is the root
of this tree and thus doesn't have a parent.
HTH
♠Thats a good description. I was however more interested in how it works? I mean what are the steps that take place for it to get active?????? I am not sure if I am phrasing my question right.