Constructing a Class from Scratch
You need to load a class and run its methods.
Write and use your own
, of course, is a program
that loads classes. There is one class loader built into the Java
Virtual Machine, but your application can create additional ones as
needed. Learning to write and run a working class loader and use it
to load a class and run its methods is a nontrivial exercise. In
fact, you rarely need to write a class loader, but knowing how is
helpful in understanding how the JVM finds classes, creates objects,
and calls methods.
ClassLoader itself is abstract; you must subclass
it to provide a
method that loads classes as you wish. It can load the bytes from a
network connection, a local disk, RAM, a serial port, or anywhere
else. Or you can construct the class file in memory yourself if you
have access to a compiler.
You must call this class loader’s
loadClass( ) method for any classes you wish to load from it. Note
that it will be called to load all classes required for classes you
load (parent classes that aren’t already loaded, for example).
However, the JVM will still load classes that you instantiate with
new operator “normally” via
To write a class loader, you need to subclass
ClassLoader and implement at least
loadClass( ). The
loadClass( ) method needs to get
the class file into a byte array (typically by reading it), convert
the array into a
Class object, ...