(FWD)Handouts for GNHLUG Oct. 30th meeting: Part I
Jerry Feldman
gaf at zk3.dec.com
Thu Oct 24 14:13:28 EDT 1996
From: Jon "Maddog" Hall <hall at zk3.dec.com>
This is the handout for Bill McKeeman's talk on Java, to be given at UNH
on October 30th at 1900 hours.
I am sending you the handouts in two parts, labeled "Handout: Part One"
and "Handout: Part Two" (hey, we don't do anything fancy, here!!), since
majordomo has a (self-imposed) limit of 44,000 characters.
[Editor's note: Can you imaging someone SPAMing a message that is *over*
44,000 characters? The mind boggles.....]
If you wish, you can print these and bring them with you to take notes.
So you expected that *I* was going to print, copy, staple and
distribute them? HA!! Dream on, McDuff!!!
md
P.S. If you think that just having the handouts is good enough, you
have never heard Bill speak. :-)
=============================================================================
Java Briefing
-- the BIG picture --
Bill McKeeman
Especially prepared for
Greater C Team Meeting 96.02.22
and updated for
The CTG Lunchtime Seminar Series 96.03.08
and updated for
Digital Galway 96.04.22
and updated for
OBB/DMQ 96.06.27
and updated for
VoiceTek 96.09.13
and updated for
Digital Unix Engineering Group 96.09.20
and updated for
The NH Linux Users Group 96.10.30
Java has been around for about 4 years, starting as a TV settop language called
OAK, and passing various internal engineering perils until SUN finally hit on
using it as a browser-side execution medium. The details of the early history
of Java are gleefully documented in many of the introductory books on Java.
What is magical about Java is that it has caught on and Gosling did a good job
of designing it. Now Guy Steele and Bill Joy did a good job of defining it.
Java has momentum. It also means that the Java world is changing daily. There
is a firehose full on information about Java in every communication medium,
most especially the WWW. One good way to get early information is to read
JavaWorld, an on line magazine devoted to current news
(http://www.javaworld.com).
There are lots of other wannabe languages to fill the role of a browser-side
execution medium (Inferno, JavaScript, VBscript, Visual Basic, etc. etc.).
The fundamental technical requirements for a Java competitor are:
1. Platform-independent execution.
2. Virus and Trojan Horse resistant.
3. Privacy respecting.
Even though Java was designed to put interactive content into WWW pages, it can
also be used for many other system tasks. Java will give C++ a stiff challenge
in the places were C++ was becoming dominant. C, other other hand, will
probably retain its role as an efficient application language and also as the
language of choice to support native methods in Java.
There are (at present) three forms to a Java program (applet, servlet and
application).
An applet (which comes down the wire from a server side and runs in the
browser) attaches methods to screen and keyboard events. The result is
interactive content without needing server intervention once execution
starts.
A servlet (which comes up the wire from the browser side and runs on
the server) is a means for the browser to request computation to be
done on the server. Servlet/applet communication is convenient because
both can work to a common API.
An application (which runs from your command line) and acts like a normal
program.
An application has a method named main which is where execution starts. There
is nothing otherwise special about the name main, which can also be present in
applets and servlets but has no effect unless it is explicitly called or
associated with a screen event. I put a main in every applet and use it to
run the applet as an application for standalone unit tests.
The fundamental change in
The World As We Know It
is that the WWW provides a new channel for software distribution (netwrap) --
Java code can be can be up or down loaded over the net. SUN is trying hard to
make Java the preferred medium for netwrap. Others (Microsoft) are trying hard
to make Java not the ONLY medium for netwrap. See conventional compilation
below.
Platform independent execution is achieved two ways. The first is by porting
the Java interpreter so that each platform is capable of efficient
interpretation of the Java executables. The second is providing platform-
specific compilers to turn Java executables into machine language, picking up a
factor of 20 or so in Java execution speed. SUN is busily turning out 25 cent
Java interpreter chips so that no platform-specific compiler is needed (see
below).
The virus problem is close enough to being solved that it is national news when
someone finds a hole in the system. Probably nothing can be done about stink
bombs, Java applets that consume system resources so fast that the user has to
do something to clean it out. But this is an annoyance, not a safety issue.
Privacy of the user's data is another area which has shown some problems. In
particular, some applets have been caught emailing data back to the applet
server.
I think nearly all of the holes will be plugged. When a new one shows up there
is a potential Black Monday where most of the PCs in the world die. A few
incidents like this could kill Java.
language competition
--------------------
Java is a competitor to C and C++. It is my opinion that the combination of
Java with C native methods is a more effective programming language model that
C++. But so are a lot of other things. That has not stopped C++ yet.
The deciding factors in language adoption are availability and investment.
There is already an enormous industry-wide investment in C++, mostly in the
form of existing applications, training and class libraries. If someone
invests in moving the C++ class libraries to Java or Java+C (see below), Java
will begin to compete in the traditional 3GL space. In any case Java use will
grow in its own niche of netware -- giving it the leverage that Pascal and
Modula never had. Also, it causes a smaller break in the utterly universal C
paradigm than did the Pascal family, which shows good business sense on the
part of the Java designers. There is no point in fighting over surface
syntax.
C won that battle years ago.
Brown University is already using Java instead of C++ in its teaching program.
I would too, if I were still teaching in a University. Java is conceptually
cleaner and simpler and richer. Good for learning concepts. Reasonable chance
of being a useful skill after graduation. Other universities are following
Brown's lead.
Another competitor is Visual Basic. I have done most of my personal computing
in Basic for years. It is lots easier to use than C. Microsoft knows this and
has 3,000,000 users who must agree. There are probably few nerds among them
and lots of business people. Again, surface syntax does not matter much. What
does matter is the supporting class libraries and mature integrated development
environment. Visual Basic is very O-O, and the infrastructure is highly
developed. See Development Tools below.
It is possible to support other languages within the Java infrastructure. SUN
has announced support for Scheme, Ada and Visual Basic. SUN has also announced
a chipset supporting Java byte codes directly, eliminating the need for the
JVM. This is an interesting development considering the industry has finally
reached a consensus on risc machines for performance. The SUN Java chips are
definitely cisc. I think older languages such as Pascal and Modula are just
not candidates anymore. There is no technical reason that they cannot be used
but Java is good enough so why bother?
In my opinion, the really interesting development will be JavaPlus -- that is,
dialects that can map onto Java. This can vary from Java plus some built in
operators and classes to a language more like Basic that makes the Java
structuring (classes, methods, ...) implicit. Such a scenario is an extension
enabled by the Java infrastructure, not competition with it.
UTF8
------------------------
One forward-looking Java feature is Unicode source input. Unicode is a
standard within which all the worlds natural languages can be encoded. It has
been ratified by most of the governments in the world, including Japan, China
and Korea, which had to agree on Kanjii (the so-called Han unification
effort). Ritchie and Pike invented an encoding for unicode that is upward
compatible with ASCII. Looking at the bit layout of the code, the trick is to
use more than one byte for some codes.
0bbbbbbb ASCII 0-127 7 bits
110bbbbb 10bbbbbb unicode 0-2047 11 bits
1110bbbb 10bbbbbb 10bbbbbb unicode 0-65535 16 bits
The code has the property that even coming in the middle you can establish the
character boundaries. Leading 10 means "in the middle of a character" Leading
0, or leading 11 means "starting a character". In the tables for unicode there
are digits for 15 different number systems, large ranges of unicode acceptable
for identifiers, and so on. The Java Language specification says that
non-ASCII cannot show up in numbers. Seems like a small oversight that may
someday be corrected. Why irritate the Tamils (or Tibetans) unnecessarily?
In fact SUN has not yet delivered on the Unicode promise by implementing the
libraries with Unicode. That is, most everything is there except input, output
and graphics :-). SUN says the 1.1 release will do better.
Now, of course, my keyboard does not include a key for Kanjii "rice paddy", but
there is a unicode escape in the form of \uxxxx, giving a 4-hex-digit value
which can be embedded in the Java source text. This solves in a single stroke
the problems that caused digraphs and trigraphs and wchar_t to show up in C.
JIS is not a subset of UTF8, so the Japanese are not going to be able to switch
(anytime soon) to UTF8 because of billions invested in JIS data and programs
with hardcoded JIS dependencies. The Japanese can and do use wchar_t.
Programming in Java
------------------------
If you are a C programmer and want to program in Java the way you program in C,
it will take an afternoon to get started. Almost all of the effort is learning
a new run-time package which has the same kind of stuff stuff as the CRTL, just
with different names.
If you are a C++ programmer and want to program in Java the way you program in
C++, it will take a week to get started. On top of having to learn the new
run-time, you also have to unlearn a lot of C++ creature comforts and syntax
and expectations.
If you want to program Java the way the designers intended, it will take six
weeks. You will have to learn two books worth of run time interfaces, and
then switch to an event-driven, thread-rich, model of programming. You have
to define lots of methods for the run time to call, but on its own initiative.
Things happen. Events occur. Your program must react correctly to all of
them. The (wonderful) freedom to abandon storage management to the garbage
collector is offset by the new problem of garbage threads that run and run
and run.
Here is an example of Java written by a C programmer (me, although this is
much like a demo program from SUN).
// FILE: tictactoe.java
// PURPOSE: java demo application to play tic-tac-toe
// MODS: mckeeman at zko.dec.com -- 95.12.20 -- original
// who at where -- yy.mm.dd -- what
// METHOD: The tic-tac-toe board is represented by two 9-bit vectors,
// one recording the X moves, and one recording the O moves.
// The correspondence between row, column and bit is b = 1<<r*3+c.
// X plays first. O moves automatically (using a weak heuristic).
// The class TicTacToe encapsulates the board and strategy.
// The class Play provides main() and the play-by-play interaction.
import java.io.*; // for println
class BadMove extends Exception { // for throw
BadMove() { super(); }
}
class TicTacToe extends Object {
// all eight winning combinations
final int[] wins = {0007,0070,0700,0111,0222,0444,0124,0421};
// center is best, corners next, edges are last choice
final int[] best = {0020,0100,0400,0001,0004,0200,0010,0040,0002};
private int X, O; // record of moves
public TicTacToe () {X = 0000; O = 0000;} // initialize
private boolean
taken(int move) { // move not available
return ((X|O)&move) == move;
}
private boolean
win(int board) { // XXX or OOO
for (int i=0; i<wins.length; i++) {
int w = wins[i]; // three in a row
if ((board&w) == w) return true; // win
}
return false; // not win
}
public boolean Xwin() {return win(X);} // X won?
public boolean Owin() {return win(O);} // O won?
public boolean cat() {return ((X|O) == 0777);} // no more moves
// make pretty output for tic tac toe board
public String
picture() {
String b = ""; // empty to start
for (int r=0; r<3; r++) { // rows
for (int c=0; c<3; c++) { // column
int m = (int) (1 << r*3+c); // convert to linear
if ((X&m)==m) b += "X"; // an X
else if ((O&m)==m) b += "O"; // an O
else b += "."; // empty square
}
b += "\n"; // end of row
}
return b; // picture of board
}
// do what the player requests
public void
ex(int r, int c) throws BadMove {
int m = (int)(1 << r*3+c); // row-col conversion
if (taken(m)) throw new BadMove(); // reject move
X |= m; // update X moves
}
// simple-minded computer opponent
public void
oh() {
for (int t=1; t<=0777; t<<=1) { // look for O win
if (!taken(t) && win(O|t)) {O |= t; return;}
}
for (int t=1; t<=0777; t<<=1) { // look for X win
if (!taken(t) && win(X|t)) {O |= t; return;}
}
for (int i=0; i<best.length; i++) { // look for move
int t = best[i]; // best first
if (!taken(t)) {O |= t; return;} // update O moves
}
}
}
class Play extends Object {
// io routines
private static void
output(String s) throws IOException {
System.out.println(s); //print line
}
private static int
input(String prompt) throws IOException {
output(prompt);
while (true) {
char r = (char) System.in.read(); // a keystroke
if ('0' <= r && r <= '2') { // valid?
output(""); // signal acceptance
return Character.digit(r, 10); // convert and return
}
if (r == '\n' || r == ' ') continue; // ignore whitespace
output("enter 0,1 or 2 please: "+prompt); // complain
}
}
// main program
public static void
main(String argv[]) throws IOException {
TicTacToe ttt = new TicTacToe(); // new board
while (true) {
int r = input("row = ?"); // user input
int c = input("col = ?");
try {
ttt.ex(r, c); // user move
output(ttt.picture()); // display results
} catch (BadMove e) {
output("square "+r+","+c+" occupied, try again");
continue; // try again
}
if (ttt.Xwin()) { // X wins?
output("X wins"); // notification
break;
}
if (ttt.cat()) { // cat wins?
output("cat game"); // notification
break;
}
ttt.oh(); // machine move
output(ttt.picture());
if (ttt.Owin()) { // O wins?
output("O wins"); // notification
break;
}
}
}
}
JavaScript, etc.
---------------------------------------------
JavaScript is a language (from NetScape, previously called LiveScript) which
can be embedded between html <script>...</script> tags in pages prepared for
the NetScape browser. It does not need compilation, which makes it a good deal
easier to use than Java. Executing JavaScript is slower than executing Java
byte codes which, in turn, is slower than machine code. JavaScript is also
less capable. It looks and feels a lot like tcl/TK to me, dressed up in Java
clothing. One can think of a JavaScript as the inside of a single Java method
with predefined hooks for screen events (like Click). The screen layout itself
is done in HTML with tags like <input>. JavaScript can call into Java.
Microsoft claims to be working on VBscript, a strict subset of Visual Basic, as
a competitor to JavaScript.
SUN is talking about using tcl/TK as a WWW scripting language. The author,
Ousterhaut, quit UC Berkeley to work for SUN about two years ago.
the WINNER
---------------------------------------------
I believe that most simple interactive content in HTML is going to be in the
scripting languages. JavaScript is not a carefully thought out language but it
is established. Microsoft can probably force VBscript on everyone by just
making it available in their favorite web browser. Ease of use will win all to
the scripting language (except the nerd market). Java is easier than C++ but
so is jumping off a bridge.
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