Transcript poosd-H.ppt

Principles of Object-Oriented
Software Development
Hello (CORBA) Universe
Hello (CORBA) Universe
Introduction
Interface
The broker abstraction
C++ Realization
Java Realization
Prolog Realization
Configuration
Conclusions
Hello (CORBA) Universe
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platform-independent
language-independent
server -- C++, Java, Prolog, ...
client -- C++, Java, Prolog, ...
9 combinations -- test.sh
The Interface - IDL
module universe {
interface world {
void hello();
void ask(in string x);
string tell();
oneway void halt();
};
};
universe.idl
world
C++ Realization
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broker -- access to ORB and BOA
client -- needs ORB only
server -- needs access to BOA
implementation -- world-srv.h world-srv.c
C++ broker -- class
class broker {
public:
broker();
void init(int& argc, char**& argv, int fl=0);
int operator()();
broker.h
1 = client
to run the server
char* ref(corba::object* x);
object_to_string
corba::object* ref(const char* s);
string_to object
corba::object* object(const char* file);
get object IOR file
void refout(const char* f, corba::object* x);
IOR to file
};
C++ broker -- implementation
broker::broker() { }
broker.c
void broker::init(int& argc, char**& argv, int fl=0) {
_orb = CORBA_ORB_init(argc, argv);
if (!fl) _boa = _orb -> BOA_init(argc, argv);
}
}
int broker::operator()() {
_boa -> impl_is_ready(CORBA_ImplementationDef::_nil());
}
int main(int argc, char* argv[], char*[]) {
broker* _broker = new broker();
try
{
_broker->init(argc,argv);
client.c
get yourself a broker
initialize broker
corba::object* obj = _broker->object("world.ref");
universe_world_var world = universe_world::_narrow(obj);
{
some object invocations
world -> hello();
world -> ask("How are Clinton's affairs?");
cout << "client:" << world->tell() << endl;
}
} catch(corba::exception ex) { ... }
}
int main(int argc, char* argv[], char*[])
{
broker* _broker = new broker();
try
{
_broker->init(argc,argv);
server.c
get yourself a broker
initialize orb and boa
universe_world_var p = new universe_world_srv;
_broker->refout("world.ref", p);
_broker->operator()();
}
catch(corba::exception& ex) { ... }
}
write identity
run the the world
void universe_world_srv::hello() {
cout << "Hello World!" << endl;
}
void universe_world_srv::ask(const char* s) {
cout << "Asking: " << s << endl;
}
char* universe_world_srv::tell() {
char result[] = "ok";
CORBA_String_var s = (const char*) result;
return s._retn();
}
void universe_world_srv::halt() {
exit(0);
}
world_srv.c
Java Realization
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broker -- contact ORB and BOA
client -- connect to server
server -- announce server object
implementation -- world_srv.java
import org.omg.CORBA.*;
import java.io.*;
public class broker {
boolean _fl = false;
java.applet.Applet _applet = null;
public broker() { }
public broker(boolean fl) { _fl = fl; }
public broker(java.applet.Applet x) {
_applet = x;
init(null);
}
broker.java
public void init(String[] args) {
if (_applet == null) {
_orb = ORB.init(args,new java.util.Properties());
if (!_fl)
_boa = _orb.BOA_init(args,new java.util.Properties());
} else
_orb = ORB.init(_applet, null);
}
public int operator() {
run -- server-only
if (!_fl) _boa.impl_is_ready(null);
return 0; // OK
}
....
};
Java -- broker
package universe;
import org.omg.CORBA.*;
import java.io.*;
import hush.broker;
client.java
see broker.java
public class client {
public static void main(String args[]) {
broker _broker = new broker(true); // true means client only
try {
_broker.init(args);
init orb
org.omg.CORBA.Object obj = _broker.object("world.ref");
world world = worldHelper.narrow(obj);
if (world == null)
throw new RuntimeException();
System.out.println("Enter 'h' for hello or 'x' for exit:");
... // do some requests to the world
} catch(...) { ... }
} };
package universe;
import org.omg.CORBA.*;
import java.io.*;
import hush.broker; // see broker.java
public class server
{
public static void main(String args[])
{
broker _broker = new broker();
try
{
_broker.init(args);
world_srv p = new world_srv();
_broker.refout("world.ref",p);
server.java
create orb en boa;
create impl object
write ref
// create world.htm
_broker.html("world.htm",p,
" code=universe/applet.class " +
"width=500 height=300");
_broker.operator();
// run == boa.impl_is_ready(null);
} catch(SystemException ex) {
_broker.print(ex);
System.exit(1);
}
System.exit(0);
}
}
Java -- server
package universe;
import org.omg.CORBA.*;
public class world_srv extends _worldImplBase
{
public void hello() {
System.out.println("Hello World!");
}
public void ask(String msg) {
System.out.println(msg);
}
public String tell() {
String s = new String("ok");
return s;
}
public void halt() {
System.exit(0);
}
world_srv.java
Prolog Realization
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broker -- mediating service
client -- get object reference
server -- provide implementation
implementation -- universe.pl
broker(client(M:F)) :-
broker.pl
...
corba_initialize_orb([], _),
factory(F).
gives a handle to the server object
broker(server(M:I)) :...
corba_initialize_server([server,server(test),
timeout(infinite)],Server),
...
create server object
G =.. [_Create,_Server,Self],
call(G),
corba_object_to_string(Self,IOR),
open(IORFile,write,Fd),
format(Fd,'string',[IOR]),
close(Fd),
corba_main_loop(Server).
write reference to file
enter main loop
Prolog -- broker
client.pl
:- use_module(universe).
see universe.pl
:- [broker].
include broker
main :broker(client(universe:F)),
assert(client(factory(F))),
run.
initialize the broker
run :h,
ask('What is the state of Clinton s affairs?'),
write('Type h to say hallo, x to quit.'),nl.
ask(X) :client(factory(F)),
write(client(ask(X))),nl,
world_ask(F,X),
world_tell(F,R),
write(client(ans(R))),nl.
h :- client(factory(F)), world_hello(F).
q :- client(factory(F)), world_halt(F), halt.
x :- halt.
Prolog -- client
:- [broker].
server.pl
main :broker(server(universe:world)).
Prolog -- server
:- module('universe',[]).
universe.pl
world_hello(_Self) :write('Hello World'),nl.
world_ask(_Self, X) :write(asking(X)), nl.
world_tell(_Self,Y) :Y = 'logically, ok',
write(telling(Y)),nl.
world_halt(_Self) :halt.
Prolog -- implementation
Configure, make and test
• Makefile
• corba.cfg
• test.sh
Conclusions
• CORBA is ripe to be exploited in OO -- the
practicum
• the broker is a useful abstraction
• forget about the wiring - concentrate on
application logic
Idioms and Patterns
Introduction
Polymorphism
Idioms in hush
A catalogue of design patterns
Event-driven computation
Summary
Q/A
Literature
Summary
Questions
1.How would you characterize OOP and what, in your opinion, is the
motivation underlying the introduction of OOP?
2.Characterize the most important features of OOP.
3.Explain the meaning of the phrase "object orientation reduces the
complexity of programming."
4.How would you characterize contracts? Why are contracts important?
5.How is OOP related to programming languages?
6.What classes of languages support OOP features? Explain.
7.What influence is an object-oriented approach said to have on the
software life-cycle? What is your own opinion? Discuss the problem of
maintenance.
8.How would you characterize software quality?
9.Mention a number of object-oriented programming languages, and give
a brief characterization.
10.What do you see as the major challenges for research in objectorientation?
Further reading
Nowadays there are many books that may serve as a starting point
for reading about OO. Dependent on your interest, you may look at
[Surviving], which treats issues of OO project management,
[Meyer97], which gives an extensive introduction to design by
contract and programming in Eiffel, or [Fowler97], which gives a
succinct introduction to UML. Alternatively, you may take one of
the introductory programming books for Java, from which you will
almost certainly learn something about OO as well.