IN 104
Lecture 4
1999.9.14
Today’s lecture
• Discussion of some Java features
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event-driven programming (Zoom2 applet)
parameter input to method
load data from URL
about applet
• The StockPlotter/WeatherPlotter project
• Slides will be available at IN104 home page
Event-driven programming
• Implement “listener” - define program
response in the abstract method(s)
• Attach GUI component(s) with listener(s)
• Example
class MyListener implements ActionListener {
public void actionPerformed (ActionEvent e) { /* … */ }
}
// ...
Button knappen=new Button(“Press”);
knappen.addActionListener (mylistener);
The Zoom2 applet
• Scrollbar
• AdjustmentListener
public class Zoom2 implements AdjustmentListener
Zoom2.java (part I)
import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;
public class Zoom2 extends Applet implements AdjustmentListener {
private final int SIZE = 300;
private Scrollbar bar =
new Scrollbar(Scrollbar.HORIZONTAL, 10, 64, 10, SIZE);
private int current_size = 10;
private Image picture;
public void init() {
setLayout (new BorderLayout());
setBackground (Color.white);
bar.addAdjustmentListener (this);
picture = getImage (getDocumentBase(), "owl.gif");
add (bar, "South");
setSize (SIZE, SIZE);
setVisible (true);
} // method init
Zoom2.java (part II)
public void zoom_image (int size) {
current_size = size;
repaint();
} // method zoom_image
public void paint (Graphics page) {
page.drawImage (picture, SIZE/2-current_size/2,
SIZE/2-current_size/2, current_size, current_size, this);
} // method draw
public void adjustmentValueChanged (AdjustmentEvent event) {
zoom_image (event.getValue());
} // method adjustmentValueChanged
} // class Zoo
Parameter input to method
• Primitive data by copy
• Object data by copy of reference (alias)
• Example
class Num {
public int number;
}
// …
void work (Num num, int i)
{
num.number++; // has effect outside
i = 2;
// no effect outside
num = new Num; // no effect outside
}
Load data from URL
import java.net.URL;
import java.io.BufferedReader;
import java.io.InputStreamReader;
try {
URL url =
new URL(“http://www.stud.ifi.uio.no/~in104/Quotes/tickers.in104”);
BufferedReader reader=new BufferedReader(new
InputStreamReader(url.openStream()));
String inputLine;
while ((inputLine=reader.readLine()) != null) {
// …
}
reader.close();
} catch (Exception e) { /* … */ }
Applet life cycle
• Web browser starts JRE
• JRE loads all java binaries (*class *jar *zip)
• JRE launches the applet
<applet code=“example.class”>
• Applet’s init method - applet parameters
input, GUI + other one-time initializations
• Applet’s start method - right after “init”, also
called e.g. when browser returns to the web
page
Applet life cycle
• Applet’s stop method is called when e.g.
browser leaves the web page - should kill
computing intensive threads
• Applet’s destroy method is called before
applet is terminated
• Applet’s paint method is responsible for
updating the drawing done directly on the
Graphics object
The Response applet
• http://www.ifi.uio.no/~in104/forelesninger/L
ectures/Lecture4/Response.html
• An example showing when methods init,
start, paint, stop and destroy are invoked
• Each method increases its own counter
every time it’s invoked
Applet security
• Applet can only load data from the server it
was loaded from
• Applet normally not allowed to access the
local file system
• Exception: applets loaded from your local
system (file:/…) can read/write to the local
file system
• An applet cannot run a local executable
• Limited access to operating system info
HTML tags for applet
<applet code=“Test.class” width=300
height=200
archive=“http://www.stud.ifi.uio.no/~in104/
jars/in104.jar”>
<param name=“color1” value=“blue”>
<param name=“color2” value=“white”>
</applet>
Receiving parameters
• The Applet class has a method named
getParameter that can be used to obtain the
values assigned by the HTML <param> tag
• Example
class AppletWithParameters extends Applet
{
private String foreground, background;
public void init () {
foreground = getParameter(“color1”);
background = getParameter(“color2”);
}
// …
}
Project general info
• A sophisticated applet capable of
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loading data (stock/weather) from URL
simple graphical representation of curves
interactive GUI events
simple mathematical analysis
• A web page containing the applet
• Deadline for submission: 19. Nov. kl.12:00
(email to the group teacher)
• JDK 1.1
• IN104 java library in104.jar also allowed
Project rule & exam
• Each student should work independently
• Don’t open file protection of *.java files at
any time!
• unix>zip -ee oppgave.zip *.java
• Exam in week 48
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check “godkjent” list
meet at the usual group hour
form of “declaration”
majority examined by the group teacher
some randomly chosen students will be
examined by the lecturers
Requirements
• Applet should work as described
– user-friendly GUI
• Structured and easily understandable source
codes (*.java)
– clear data structure
– meaningful variable names
– use of comments
Project data
• Choice 1: Historical prices - different stocks
• For every chosen stock
– day close price history (day1, price1, day2, price2...)
– day sales history (day1, volumn1, day2, volumn2…)
• Choice 2: Meteorological measurements different locations
• For every chosen location
– temperature history (day1, temp1, day2, temp2…)
– precipitation history (day1, rain1, day2, rain2…)
Historical stock price data
• Ticker list file
http://www.stud.ifi.uio.no/~in104/Quotes/tickers.in104
TOTX Totalindeksen
AKE Aker RGI A
KVI
Kværner A
NTC NetCom
…
• One file per stock, e.g. TOTX is as follows
http://www.stud.ifi.uio.no/~in104/Quotes/Oslo/TOTX
02.01.97 967.63 960.72 967.63 963.71 582716
03.01.97 978.55 963.78 963.78 978.55 823148
06.01.97 992.54 978.55 978.55 992.42 1107668
07.01.97 996.20 987.54 992.42 992.65 1009872
...
Meteorological measurement
• Location list file
http://www.stud.ifi.uio.no/~in104/Met_data/locations.in104
01001 JAN MAYEN
01007 NY-ALESUND
01008 SVALBARD LUFTHAVN
01010 ANDOYA
…
• One file location, e.g. 01001 is as follows
http://www.stud.ifi.uio.no/~in104/Met_data/Norway/01001
16.06.99
4.2
5
5.4
3.9
4.1
17.06.99
5.5
3.6
2.7
2.8
9.25
18.06.99
4
3.3
3.5
1.5
3.8
19.06.99
1.8
2.6
2.6
1.7
0.25
...
GUI organization example
User response
Smoothing filters
IN104 java library - in104.jar
• Use the on-line documentation!
http://www.stud.ifi.uio.no/~in104/in104.jar.doc/packages.html
• Learn from the weekly exercises!
~in104/bin/unpack_skeleton.sh
• Include the following path into the
$CLASSPATH environment variable
/hom/in104/www_docs/jars/in104.jar
• Use the HTML ARCHIVE tag
archive=“http://www.stud.ifi.uio.no/~in104/jars/in104.jar”
Handling dates
• From String (“14.09.99”) to Date
import java.text.SimpleDateFormat;
import java.util.Date;
SimpleDateFormat parser = new
SimpleDateFormat(“dd.MM.yy”);
Date date = parser.parse(“14.09.99”);
• From Date to int (using 01.01.97 as ref.)
Date ref_date = parser.parse(“01.01.97”);
final int millisec_in_a_day = 86400000;
int day_ident = (date.getTime()
-ref_date.getTime())/millisec_in_a_day;
01.01.97 -> 0
14.09.99 -> 985
Coordinate transform
• Transform standard coordinates (x,y) to
(u,v), those accepted by class Graphics
f max y
cmin y
f min y
cmax y
f min x
f max x
cmax x  cmin x

u  s x x  t x s x  f max x  f min x

v  s y y  t y s   cmax y cmin y
f max y  f min y
 y
cmin x
cmax x
t x  cmin  f min x
x


t y  cmax y  f min y

cmax x  cmin x
f max x  f min x
cmax y  cmin y
f max y  f min y
Smoothing filters
• Piecewise linear least square approximation
• Gliding average (xj,yj), j=1,…,m
• (ai,bi), i=1,…,m-n+1
a i  xi  n 1
bi 

i  n 1
j i

yj n
• Cubic spline interpolation/approximation