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java-interest-digest Thursday, 21 September 1995 Volume 01 : Number 178
In this issue:
File object questions
GraphicsTest demo applet bug?
User machine resident data and code
Re: method/fn ptrs?
Re: Question: JDK problem.
Re: NetScape and Java
Re: method/fn ptrs?
Re: AWT Menu Events
Re: looking for yacc specification of Java
Change Management
throws declataration in Java/beta
----------------------------------------------------------------------
From: john@anasazi.com (John Moore)
Date: Wed, 20 Sep 95 16:59:32 -0700
Subject: File object questions
(1)Is there any way to open a file and append to it? Any stream-like
graceful way a-la UNIX?
(2)Is there any direct way to write a string to an output stream other than
by copying it to a byte array and then writing that?
------------------------------
From: egrossma@ncsa.uiuc.edu (Ed Grossman)
Date: Wed, 20 Sep 1995 18:59:29 -0500
Subject: GraphicsTest demo applet bug?
The GraphicsTest demo displays a number of shapes, and allows the user to
choose which shapes. It looks like the shapes are being clipped on the
top, as if the button bar were being drawn over them. If the button bar is
moved from "North" to "South" there is no longer any clipping. I'm
wondering if anyone else has noticed this, and ascertained what exactly is
causing it. As far as I can tell, the coordinates for the button bar and
the panel holding the shapes are correct, leading me to believe the problem
is not with the layout object. I'm particularly puzzled because it is not
at all clear how the Panel object draws its children - there is a
paintComponents call in the Container object, but it is not called from any
of the java code. So I'm wondering if this behavior is being caused by one
of those mystery peer objects. Can anyone tell?
- -- Ed Grossman
NCSA
------------------------------
From: john@anasazi.com (John Moore)
Date: Wed, 20 Sep 95 17:25:03 -0700
Subject: User machine resident data and code
I would like to be able to make an applet/application that is used as follows:
(1) I click on a web page and the applet is downloaded (if this is the first
time), or just those classes that are out of date (if this is a later time)
because the rest are kept on the client. I think this cacheing will be
important because it takes so long to load multiple classes across the
ever-slower internet. Also, my Windows95 Hotjava browser seems to load
classes one at a time, which takes even longer since the TCP set-up time is
usually longer than the download time.
(2) I fire up my Hotjava (or Hotscape or whatever it is) and this new applet
is now on my hot-list or my local home page (by magic... I want this to
happen automagically).
(3) I click on this applet and it gives me a form (another aside: what sort
of forms handling will be available?). I fill it in and the applet surfs the
web a bit for me, based on data from the previous time I ran it. It gets
some stuff, interacts with me, and hangs onto some data for the next time.
It is basically
behaving as a software agent with local, persistent storage.
The issues here are (at least):
-download time for classes
-persistent class caches on clients
-applet inserting itself into the visible world of the browser (obviously this
would have to be tightly controlled)
-storage at the client of applet-specific data that is persistent between
sessions. This is a important from both a security and applications
viewpoint.
-new security issue: a specific applet should be able to:
(a) create it's OWN directory that no other applet can access, but that can
be freely accessed by future instances of this applet.
(b) keep data in that directory that cannot be accessed by any other applet
(c) be authenticatable, and have the ability for classes that it depends
on to be authenticated.
This security issue is critical for my real-world application. I want to be
able to store, for example, credit card information on the local client, and
I certainly don't want some other application - say, a hacked version of the
eating philosophers (GREAT program btw) - to grab that information and pass
it back down the net. At the same time, I don't want the user to have to
answer authentication pop-up boxes every time the applet needs to do things.
We need the concept of an authenticatable application,
with persistent, authenticatable class cacheing, and with local persistent
storage of data that is inextricably tied to the authenticated
application (at
least from within the Java virtual machine).
Other than that, I don't want much :-)
So, Java-wizards, am I smoking the wrong thing? Have you guys been thinking
along these lines?
------------------------------
From: Sami.Shaio@Eng.Sun.COM (Sami Shaio)
Date: Wed, 20 Sep 1995 15:44:35 -0700
Subject: Re: method/fn ptrs?
There is no direct equivalent in Java. What you can do is create a
class, for example Action, that has an execute method. You then
have an array of Action objects which you can call execute on.
- --sami
|From fgreco@lehman.com Wed Sep 20 15:28:27 1995
|Date: Wed, 20 Sep 95 10:26:05 EDT
|From: fgreco@lehman.com (Frank Greco)
|To: java-interest@java.Eng.Sun.COM
|Subject: method/fn ptrs?
|X-Info: To unsubscribe, send 'unsubscribe' to
java-interest-request@java.sun.com
|
|
|Ok... how does one do the equivalent of fn-ptrs in Java?
|
|I need to save an array of ptrs-to-methods, or whatever
|the equivalent is.... am I thinking C-ish too much here?
|
|Thanks,
|
|Frank G.
|-
|Note to Sun employees: this is an EXTERNAL mailing list!
|Info: send 'help' to java-interest-request@java.sun.com
|
------------------------------
From: tball@scndprsn.Eng.Sun.COM (Thomas Ball)
Date: Wed, 20 Sep 1995 18:19:06 -0700
Subject: Re: Question: JDK problem.
The symbol char_arraycopy isn't found anywhere in the JDK release.
I suspect you have an older Java environment which is getting mixed
in. Try running:
% xhost <your display name>
% env - DISPLAY=:0.0 ../../bin/appletviewer -debug example1.html
The env command with the dash option runs the command without any
environment variables set -- DISPLAY is the only required one.
Tom
> From daemon@java Wed Sep 20 15:21:00 1995
> To: java-interest@java
> Subject: Question: JDK problem.
> X-Info: To unsubscribe, send 'unsubscribe' to
java-interest-request@java.sun.com
>
>
> Hi I just downloaded JDK and uncompressed it.
>
> Tried running appletviewer on example1.html as specified in the
> README.
>
> Heres what happens on the first example I try :
>
> > ../../bin/appletviewer -debug example1.html
> Loading jdb ...
> . Uncaught exception of type java.lang.NullPointerException
> java.lang.UnsatisfiedLinkError char_arraycopy
> at java.lang.StringBuffer.append(StringBuffer.java)
> at java.tools.ttydebug.TTY.main(TTY.java:1201)
>
>
> Did I miss something ? Am running on Solaris ..
>
> - Chanda Dharap
> ----------------
> email: chanda@prpa.philips.com
>
> -
> Note to Sun employees: this is an EXTERNAL mailing list!
> Info: send 'help' to java-interest-request@java.sun.com
>
------------------------------
From: weilerj@std.teradyne.com (Jason Weiler)
Date: Wed, 20 Sep 1995 18:23:13 -0700
Subject: Re: NetScape and Java
> > That's why Netscape would need to buy it. Otherwise, as with HTML,
> > they could just take it, couldn't they? ;-)
>
> I understand your reasoning. However, I doubt the Netscape people want the
> added burden of developing the Java language (compiler, interpreter, etc.).
> That's a lot of additional work that they probably don't need.
>
> --- SER
True, but by owning Java, they would have something that no other browser
could do. They would have a hold on the market. However, I just don't
see this happening. I wonder if Billy Gates is paying attention ;-)
- -Jason W
<weilerj@std.teradyne.com>
------------------------------
From: jpayne@starwave.com (Jonathan Payne)
Date: Wed, 20 Sep 1995 18:32:22 -0700
Subject: Re: method/fn ptrs?
Hi Sami,
Nothing personal ... :-) but
Translation: Give it up!
Could you imagine implementing emacs-style keymaps in Java? You'd
have to implement a KeyAction subclass for each command you want to
bind to a key. And each one of those subclasses would probably make a
call to another object that implements all that commands, since they
would probably rather be all together.
It's also a problem for handling callbacks from GUI controls. Right
now we have to overload methods with the object making the callback,
and that sort sucks in a number of ways. What if you want slider1 to
call one routine and slider2 to call another? Now you have to switch
in the callback to see which one it is. What if you have a new kind
of GUI object that's making a callback. The only way to make that
work is to implement the new GUI to know who it's calling back, so
that it can explicitely call the right method that's defined in that
one class ...
The language needs method pointers. Life sucks without them.
> Date: Wed, 20 Sep 1995 15:44:35 -0700
> From: Sami.Shaio@Eng.Sun.COM (Sami Shaio)
> X-Sun-Charset: US-ASCII
> Sender: owner-java-interest@java.sun.com
> Precedence: bulk
> X-Info: To unsubscribe, send 'unsubscribe' to
java-interest-request@java.sun.com
> Content-Type: text
> Content-Length: 909
>
> There is no direct equivalent in Java. What you can do is create a
> class, for example Action, that has an execute method. You then
> have an array of Action objects which you can call execute on.
>
> --sami
>
------------------------------
From: Sami.Shaio@Eng.Sun.COM (Sami Shaio)
Date: Wed, 20 Sep 1995 16:30:44 -0700
Subject: Re: AWT Menu Events
|From NickR@silverplatter.com Wed Sep 20 16:03:44 1995
| My current questions is how do I get notified when a menu item is
| selected. Looking at the HotJava alpha 3 source it uses the selected
| method of the menu class but the prebeta awt does have such a method,
| what do I use instead ?
|
See attached program below.
| On a more general note, learning the awt would be eased if an overview
| document describing its overall structure, event handling mechanism
| etc was available, is such a beast on the way ? A sample program that
| used the prebeta awt to create a app would also be useful.
|
Yes, better docs are on the way including an overview and tutorial for
awt. We just wanted to put this stuff out to get feedback before the
docs were ready since good docs take time to write.
| Are there any plans to add the ability to store text strings, menus
| etc in a seperate resource file to java ? This is needed to ease
| internationalisation of java applications.
|
There is a property method, System.getProperty that will get used for
this purpose. It still needs some fleshing out but that is its intent.
| many thanks,
|
| Nick Roberts
|
Here's a simple awt program that puts up a menubar and prints out the
contents of a menu item when selected. Compile it with javac and then
just run it as "java MenuTest":
import java.awt.*;
public class MenuTest extends Frame {
public MenuTest() {
super("MenuTest"); // set the title of the frame
MenuBar mb = new MenuBar();
// add a simple menu
Menu m = new Menu("Numbers");
m.add(new MenuItem("one"));
m.add(new MenuItem("two"));
m.add(new MenuItem("three"));
// add a submenu
Menu submenu = new Menu("More Numbers");
submenu.add(new MenuItem("four"));
submenu.add(new MenuItem("five"));
m.add(submenu);
setMenuBar(mb); // install this menu bar in the frame
resize(300, 300);
show();
}
public boolean handleEvent(Event evt) {
if ((evt.id == Event.ACTION_EVENT) && (evt.target instanceof MenuItem)){
System.out.println(evt.target.getLabel());
}
}
public static void main(String args[]) {
new MenuTest();
}
}
| *******************************************************************
|
| SilverPlatter Information Ltd Phone : +44-(0)181-995-8242
| 10 Barley Mow Passage Fax : +44-(0)181-995-5159
| Chiswick Email : nickr@silverplatter.com
| London W4 4PH Compuserve : 100014,2166
| United Kingdom
|
| *******************************************************************
|
|
|
|-
|Note to Sun employees: this is an EXTERNAL mailing list!
|Info: send 'help' to java-interest-request@java.sun.com
|
------------------------------
From: Simon Spero <ses@tipper.oit.unc.edu>
Date: Wed, 20 Sep 1995 15:16:28 -0700 (PDT)
Subject: Re: looking for yacc specification of Java
On Wed, 20 Sep 1995, Arthur van Hoff wrote:
>
> Guy Steele is working on a new Language Spec. It will contain an LALR grammar
> for Java.
And will be 1,100 long :-)
Simon
------------------------------
From: stephen@macquarie.com.au (Stephen O'Gallagher)
Date: Thu, 21 Sep 95 14:22:38 EST
Subject: Change Management
Frank Greco wrote
>> > 6. Does Java have a mechanism of versioning classes? That is, how can
>> > a user of a Java app[let] continue to use an older version of a
>> > particular class when I (as app author) upgrade my app[let].
>> > Excuse the gross analogy, but is there an equivalent of
>> > LD_LIBRARY_PATH for Java classes?
>>
>> We currently don't have a good mechanism for versioning classes. You can
>> achieve a reasonable versioning scheme using naming conventions, but that is
>> far from ideal.
>
>
>. This is important. Hint: Microsoft doesn't have a way of versioning
> .dll's and its biting them in the corporate IS/IT/MIS (gawd, its tough
> to be politically correct) world.
If you guys really expect this stuff to fly* then a lifecycle model is abs.
necc.
You need to be able to version the classes
try this keyword
version xx.yy.zz
where incremental zz's are for new versions of the class that do not
change interface
yy is for extentions of interface (ie a higher yy version can always be
used as a replacement for a lower one).
xx is used for interface incompatibility issues.
This is simple but what you really want to do is to make package a more tangible
concept than simply a directory.
You need to be able to say something along the lines of
package fred vesion 1.0.1 is
class x version 1.2.8
class y version 3.6.9
maybe you can do something with the loader to make this an optional extra but
the
class version embeded in the bytecode is a must.
Change Management is one of my favourite issues ( and one which has been handled
badly by software providers). I would be very interested in helping to frame a
CM system for Java if anyone out there is interested.
Stephen O'Gallagher
Macquarie Bank Ltd
Sydney Australia
* by 'fly' I mean take out C++ and Smalltalk as languages of choice for general
programming.
------------------------------
From: "Paul Ambrose" <pambrose@weblogic.com>
Date: Wed, 20 Sep 1995 23:17:35 +0000
Subject: throws declataration in Java/beta
Can someone please confirm the following:
In beta Java, if object A extends object B, and both implement method
foo(), A.foo() *cannot* throw exception X unless B.foo() also
throws X. If you declare that A.foo() throws X, the compiler
will complain that B doesn't also throw X.
This means that you can NEVER throw an exception from a
toString() method because Object.toString() doesn't throw
any exceptions.
Is this correct?
Paul
------------------------------
End of java-interest-digest V1 #178
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