Java in a Nutshell, 5th Edition [Electronic resources] نسخه متنی

This interface is the main entry
point to the java.lang.instrument API. A Java
instrumentation

agent specified on the Java
interpreter command line with the -javaagent
argument must be a class that defines the following method:

public static void premain(String args, Instrumentation instr)

The Java interpreter invokes the premain(
)
method during startup before calling the main(
) method
of the program. Any arguments specified with the
-javaagent command line are passed in the first
premain( ) argument, and an
Instrumentation object is passed as the second
argument.

The most powerful feature of the Instrumentation
object is the ability to register
ClassFileTransformer objects to augment or rewrite
the byte code of Java class files as they are loaded into the
interpreter. If isRedefineClassesSupported(
) returns
true, you can also redefine already-loaded classes
on the fly with redefineClasses(
).

getAllLoadedClasses(
) returns an array of all
classes loaded into the VM, and getInitiatedClasses(
) returns an array of classes
loaded by a specified ClassLoader.
getObjectSize( )
returns an
implementation-specific approximation of the amount of memory
required by a specified object.

public interface

Instrumentation {
// Public Instance Methods
void

addTransformer (ClassFileTransformer

transformer );
Class[ ]

getAllLoadedClasses ( );
Class[ ]

getInitiatedClasses (ClassLoader

loader );
long

getObjectSize (Object

objectToSize );
boolean

isRedefineClassesSupported ( );
void

redefineClasses (ClassDefinition[ ]

definitions ) throws ClassNotFoundException,
UnmodifiableClassException;
boolean

removeTransformer (ClassFileTransformer

transformer );
}