Re: Getting a reference to caller object
On Nov 27, 3:46 am, Lew <no...@lewscanon.com> wrote:
Eric Sosman writes:
public class Piotr {
public static void main(String[] unused) {
System.out.println(hello()); =
(...)
// What is the "caller object" here?
Stefan Ram wrote:
The closest approximation to an answer to the above
question might be =BBPiotr.class=AB.
(But I do not know whether such an object is instanciated
when the class =BBPiotr=AB is initialized or only when such
an object is first needed.)
The class object comes into existence when the class is loaded, but not a=
ll
class initialization happens then. The 'class' attribute is an attribu=
te of
the class object, not the class object itself. The VM loader loads and
initializes the class 'Piotr' and calls its 'main()', and thus 'Piotr',
running 'main()', is the caller of 'hello()'.
The class is loaded upon first reference to it or its members, but not
necessarily initialized right then. For example, a reference to 'Piotr=
..class'
will load 'Piotr' if it wasn't already, but not initialize it.
The invocation of 'main()' will cause class initialization, so that will =
have
happened before the call to 'hello()'.
--
Lew
Hi guys,
Thanks, but this is not what I want; I would like something like the
program below. Basically references to live objects, not class
definition objects. It is for easier troubleshooting of an existing
large production system, if something sets up a bad status, I would
like to know what caused it, we have a lot of information in JMX
already to click through, but not real stacks - and you cannot really
debug a live production system.
By debugger I mean debugger, like Eclipse debugger - you can see all
stack frames, local variables in them, and "this" local to each stack
frame, so you see values of fields in each object in stack frames,
from your breakpoint location all the way up to top level Thread.run()
or similar.
Cheers,
Piotr
class A {
int i, j;
void a() {
i = 1;
j = 2;
aa();
}
void aa() {
B b = new B();
b.b(this);
}
}
class B {
void b(Object o) {
// assuming Magic.getStackFrame(thread, nextFrame - null means we are
asking for the last frame in stack)
// getting first from stack frame
Frame frame1 = Magic.getStackFrame(Thread.currentThread(), null);
// THIS IS WHAT I WANT TO RETRIEVE, FROM HERE
assert(frame1.objectRef == o);
assert(A.class.getDeclaredField("i").get(frame1.objectRef) == 1);
assert(A.class.getDeclaredField("j").get(frame1.objectRef) == 2);
// TO HERE
// we were called from no arg method - this is retrieveable from
// Thread.dumpStack() actually
assert(frame1.method.equals(A.class.getMethod("aa", new Class[]
{Object.class})));
Frame frame2 = Magic.getStackFrame(Thread.currentThread(), frame1);
assert(frame2.objectRef == frame1.objectRef); // the same object,
also not retrievable using what I know
assert(frame2.objectRef == o);
assert(frame1.method.equals(A.class.getMethod("a", new Class[]{})));
Frame frame3 = Magic.getStackFrame(Thread.currentThread(), frame2);
assert(frame3.objectRef == null); // this method was called from
static method
assert(frame3.method.equals(C.getMethod("main"), new Class[]
{String[].class}));
Frame frame4 = Magic.getStackFrame(Thread.currentThread(), frame3);
assert(frame4 == null); // it was top level frame
// etc.
}
}
class C {
public static void main(String s[]) {
new A().a();
}
}