Download APPLET - aut.upt.ro

OBJECT ORIENTED
PROGRAMMING
Course 9
Loredana STANCIU
[email protected]
Room B613
APPLETS
A program written
itt in
i th
the JJava programming
i
language that can be included in an HTML
page
´ A special kind of Java program that a
browser enabled with Java technology can
d
download
l d ffrom th
the iinternet
t
t and
d run
´ Embedded inside a web p
page
g and runs in the
context of a browser
´ Extends the Applet class
´
LIFE CYCLE OF AN APPLET
´
´
´
´
init():
i
i () intended
i t d d ffor whatever
h t
iinitialization
iti li ti iis
needed for the applet
start(): automatically called after init() and
whenever user returns to the page containing the
applet after visiting other pages
stop():
p() automaticallyy called whenever the user
moves away from the page containing applets or to
stop
p an animation
destroy: called when the browser shuts down
normally.
normally
LOADING APPLETS IN A WEB PAGE
<applet
l t code=AppletWorld.class
d
l t
ld l
width="200" height="200">
´ </applet>
´
appletviewer
l t i
A l tW ld ht l
AppletWorld.html
´ when making
g changes
g to the applet's
pp
code
while it is loaded in the browser, then
recompile the applet and press the "Shift
Shift +
Reload" button in the browser to load the
new version
´
GETTING STARTED WITH APPLETS
´
´
´
´
import
i
t java.applet.*;
j
l t *
import java.awt.Graphics;
public
bli class
l
H ll W ld extends
HelloWorld
t d Applet
A l t {
« public void paint(Graphics g) {
² g.drawRect(0,
0 0
0, getSize().width - 1,
1
getSize().height - 1);
² g.drawString("Hello
d
St i ("H ll world!",
ld!" 5,
5 15);
15)
« }
}
GETTING STARTED WITH APPLETS
´
´
Managed
M
d and
d run b
by Java
J
Plug-in
Pl i
Extends the functionality of a web browser, allowing
applets to be run under Sun's Java(TM) SE Runtime
Environment (JRE) rather than the Java Runtime
Environment that comes with the web browser
CONVERTING APPLICATIONS TO APPLETS
An application:
A
li ti
a standalone
t d l
program
consisting of at least one class with a main
method.
´ Applets
´
« do
not have a main method
« several
methods are called at different points in
the execution of an applet
´
The difference between Java applets and
applications lies in how they are run
CONVERTING APPLICATIONS TO APPLETS
´
Create
C
t a subclass
b l
off
java.applet.Applet and override the
init method to initialize the applet's
resources the same way the main method
initializes the application's resources.
´
init might be called more than once and should
be designed accordingly. The top-level Panel
needs to be added to the applet in init; usually it
was added to a Frame in main.
OVERRIDING APPLET
APPLET’S
S METHODS
´
init()
« useful
for one-time initialization that doesn't take
very long
« contains the code normally put into a constructor
´
start()
´
every applet that does something after
i iti li ti ((exceptt iin di
initialization
directt response tto user
actions) must override the start method
´
either performs the applet's work or (more likely)
starts up one or more threads to perform the
work
OVERRIDING APPLET
APPLET’S
S METHODS
´
stop()
t ()
« most applets that override start should also
override the stop method.
« suspend
p
´
the applet's
pp
execution,, so that it doesn't
take up system resources when the user isn't
viewing
g the applet's
pp
p
page
g
destroy()
« available
for applets that need to release
additional resources.
USING THE PAINT METHOD
´
Used to draw the applet's
pp
representation
p
within a
browser page
´
public void p
p
paint(Graphics
(
p
g) {
« /*Draw a Rectangle around the applet's
display area.*/
« g.drawRect(0, 0, getWidth() - 1,
getHeight() - 1);
« /*Draw the current string inside the
rectangle.*/
« g.drawString(buffer.toString(), 5, 15);
}
´
The Graphic class
Is the abstract base class for all graphics
contexts that allow an application to draw
onto components that are realized on various
devices
´ A Graphics object encapsulates state
information needed for the basic rendering
operations that Java supports
´
The Graphic class
´
This state information includes the following
properties:
«
The Component
p
object
j
on which to draw.
«
A translation origin for rendering and clipping
coordinates.
The current clip.
The current color.
The current font.
The current logical
g
p
pixel operation
p
function ((XOR or
Paint).
The current XOR alternation color
«
«
«
«
«
The Graphic class
´
All coordinates that appear as arguments to
the methods of this Graphics object are
considered relative to the translation origin of
this Graphics object prior to the invocation
off the method.
The Graphic class
´
public
bli void
id t
translate(int
l t (i t x, int
i t y)
)
« Translates
´
the origin of the graphics context to
the point (x, y) in the current coordinate system
public Color g
p
getColor()
« Gets
´
this graphics context's current color.
public void setColor(Color c)
« Sets
this graphics context's current color to the
specified
ifi d color.
l All subsequent
b
t graphics
hi
operations using this graphics context use this
specified
ifi d color.
l
The Graphic class
´
public Font getFont()
« Gets
´
the current font.
public
bli void
id setFont(Font
tF t(F t font)
f t)
« Sets
´
this graphics context's font to the specified
font. All subsequent text operations using this
graphics context use this font.
public void drawLine(int x1, int y1,
int x2, int y2)
« Draws
a line, using the current color, between the
points (x1, y1) and (x2, y2) in this graphics
context's coordinate system.
The Graphic class
´
public
bli void
id drawRect(int
d
R t(i t x, int
i t y,
int width, int height)
« Draws
´
the outline of the specified rectangle. The
rectangle is drawn using the graphics context's
current color.
public void clearRect(int x, int y
p
y,
int width, int height)
« Clears
the specified rectangle by filling it with the
background color of the current drawing surface.
This operation does not use the current paint
mode.
The Graphic class
´
p
public
abstract void drawOval(int x,
int y, int width, int height)
« Draws
´
the outline of an oval.
oval The result is a circle
or ellipse that fits within the rectangle specified
by the x, y, width, and height arguments.
public abstract void drawArc(int x,
int y,
y int width,
width int height,
height
int startAngle, int arcAngle)
« Draws
D
th
the outline
tli off a circular
i l or elliptical
lli ti l arc
covering the specified rectangle. Angles are
i t
interpreted
t d such
h th
thatt 0 degrees
d
iis att th
the 3 o'clock
' l k
position
The Graphic class
´
public
bli void
id drawString(String
d
St i (St i
str,
t
int x, int y)
«
´
Draws the text given by the specified string, using this
graphics context's current font and color. The baseline of
the leftmost character is at position (x
(x, y) in this graphics
context's coordinate system.
public abstract void drawPolygon
(int[] xPoints, int[] yPoints,
int nPoints)
« Draws
a closed polygon defined by arrays of x
and
d y coordinates.
di t
E
Each
h pair
i off ((x, y)) coordinates
di t
defines a point.
The Color class
´
´
Used
U
d encapsulate
l t colors
l
iin th
the d
default
f lt sRGB
RGB color
l
space
Predefined values for colors:
« BLACK,, BLUE,, CYAN,, DARK GREY,, GREY,,
GREEN, LIGHT GREY, MAGENTA, ORANGE,
PINK,, RED,, WHITE,, YELLOW,,
The Applet class
Mustt be
M
b the
th superclass
l
off any applet
l t that
th t is
i
to be embedded in a Web page or viewed by
the Java Applet Viewer
´ Provides a standard interface between
applets and their environment.
´ More on
´
http://java.sun.com/j2se/1.4.2/docs/api/java/appl
et/Applet.html
The Applet tag
´
´
´
´
´
´
<APPLET
« CODEBASE = codebaseURL
« ARCHIVE = archiveList
« CODE = appletFile ...or...
or OBJECT = serializedApplet
« ALT = alternateText
« NAME = appletInstanceName
pp
« WIDTH = pixels
« HEIGHT = pixels
« ALIGN = alignment
« VSPACE = pixels HSPACE = pixels >
<PARAM NAME = appletAttribute1 VALUE = value>
<PARAM NAME = appletAttribute2 VALUE = value>
...
alternateHTML
</APPLET>
The Applet tag
´
CODEBASE = codebaseURL
«
´
OPTIONAL attribute specifies the base URL of the applet
— the directory that contains the applet's code. If this
attribute is not specified, then the document's URL is
used.
ARCHIVE = archiveList
«
OPTIONAL attribute describes one or more archives
containing classes and other resources that will be
"preloaded". The classes are loaded using an instance of
an AppletClassLoader with the given CODEBASE.
CODEBASE
The Applet tag
´
CODE = appletFile
pp
«
´
REQUIRED attribute gives the name of the file that
contains the applet's compiled Applet subclass. This file
is relative to the base URL of the applet. The value
appletFile can be of the form classname.class or of the
f
form
packagename.classname.class.
k
l
l
ALT = alternateText
«
OPTIONAL attribute specifies any text that should be
displayed if the browser understands the APPLET tag but
can'tt run Java applets
can
applets.
The Applet tag
´
NAME = appletInstanceName
pp
«
´
ALT = alternateText
«
´
OPTIONAL attribute specifies a name for the applet
instance, which makes it possible for applets on the
same page to find (and communicate with) each other.
OPTIONAL attribute specifies any text that should be
displayed if the browser understands the APPLET tag but
can't run Java applets.
WIDTH = pixels HEIGHT = pixels
«
REQUIRED attributes give the initial width and height (in
pixels) of the applet display area, not counting any
windows or dialogs that the applet brings up.
The Applet tag
´
ALIGN = alignment
g
«
´
VSPACE = p
pixels HSPACE = p
pixels
«
´
OPTIONAL attribute specifies the alignment of the applet.
The possible values of this attribute are: left, right, top,
texttop, middle, absmiddle, baseline, bottom, absbottom.
OPTIONAL attributes specify the number of pixels above
and below the applet (VSPACE) and on each side of the
applet (HSPACE).
<PARAM NAME = appletAttribute1 VALUE =
value>
«
The only way to specify an applet-specific attribute.
Applets access their attributes with the
getParameter() method.
Example — Drawing lines
´
´
´
import java.applet.*;
import java.awt.*;
public class DrawingLines extends Applet {
« int
i t width,
idth height;
h i ht
« public void init() {
² width = getSize().width;
getSize() width;
² height = getSize().height;
² setBackground( Color.black
Color black ); }
« public void paint( Graphics g ) {
²g
g.setColor(
( Color.green
g
);
² for ( int i = 0; i < 10; ++i ) {
¹ g.drawLine( width, height, i * width /
10, 0 ); } } }
Example — Drawing lines
´
<applet
<
l t width=300
idth 300 height=300
h i ht 300
code="DrawingLines.class"> </applet>
Example — Drawing Other Stuff
´
´
´
import java.applet.*;
import java.awt.*;
public class DrawingLines extends Applet {
« int
i t width,
idth height;
h i ht
« public void init() {
² width = getSize().width;
getSize() width;
² height = getSize().height;
² setBackground( Color.black
Color black ); }
« public void paint( Graphics g ) {
²g
g.setColor(
( Color.red );
² g.drawRect( 10, 20, 100, 15 );
² g.setColor( Color.pink );
² g.fillRect( 240, 160, 40, 110 );
²…
Example — Drawing Other Stuff
²…
² g.setColor(
Color.blue );
² g.drawOval( 50, 225, 100, 50 );
² g.setColor(
tC l ( Color.orange
C l
)
);
² g.fillOval( 225, 37, 50, 25 );
² g.setColor(
Color.yellow );
² g.drawArc(
g drawArc( 10, 110, 80, 80, 90, 180 );
² g.setColor( Color.cyan );
²g
g.fillArc(
( 140,
, 40,
, 120,
, 120,
, 90,
, 45 );
²…
Example — Drawing Other Stuff
²…
² g.setColor(
Color.magenta );
² g.fillArc( 150, 150, 100, 100, 90, 90 );
² g.setColor(
tC l ( Color.black
C l
bl k );
)
² g.fillArc( 160, 160, 80, 80, 90, 90 );
² g.setColor(
Color.green );
² g.drawString(
g drawString( "Groovy!",
Groovy! , 50, 150 );
«
´
}
}
Example — Drawing Other Stuff
´
The output:
Example — Mouse Input
´
´
´
´
´
´
import java.applet.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
java util *;
public class Mouse3 extends Applet implements
MouseMotionListener {
« int width, height;
« Vector listOfPositions;
« public
bli void
id i
init()
it() {
² width = getSize().width; height =
getSize().height;
g
g
setBackground(
g
Color.black );
² listOfPositions = new Vector();
² addMouseMotionListener( this ); }
…
Example — Mouse Input
«
«
«
public void mouseMoved( MouseEvent e ) {
² if ( listOfPositions.size()
li tOfP iti
i () >
>= 50 )
¹ listOfPositions.removeElementAt( 0 );
² repaint();
² e.consume();}
public void mouseDragged( MouseEvent e ) { }
public void paint( Graphics g ) {
² g.setColor( Color.white );
² for
f
( int
i t j = 1
1; j < listOfPositions.size();
li tOfP iti
i () ++j )
{
¹ Point A = (Point)(listOfPositions.elementAt(j1));
¹ Point B =
(Point)(listOfPositions elementAt(j));
(Point)(listOfPositions.elementAt(j));
¹ g.drawLine( A.x, A.y, B.x, B.y ); } } }
Example — Keyboard Input
´
´
´
´
import java.applet.*;
i
import
t j
java.awt.*;
t *
import java.awt.event.*;
public class Keyboard1 extends Applet implements
KeyListener, MouseListener {
« int width, height; int x, y; String s = "";
« public void init() {
² width = getSize().width; height =
getSize().height;
² setBackground( Color.black );
² x = width/2; y = height/2;
² addKeyListener( this );
² addMouseListener( this );
²}
²…
Example — Keyboard Input
«
«
«
«
«
«
«
«
«
…
public
bli void
id keyPressed(
k P
d( KeyEvent
K E
t e ) { }
public void keyReleased( KeyEvent e ) { }
public void keyTyped( KeyEvent e ) {
² char c = e.getKeyChar();
² if ( c != KeyEvent.CHAR_UNDEFINED ) {
¹ s = s + c;
¹ repaint();
¹ e.consume();
() } }
public void mouseEntered( MouseEvent e ) { }
public
pub
c void
o d mouseExited(
ouse
ted( MouseEvent
ouse e t e ) { }
public void mousePressed( MouseEvent e ) { }
public void mouseReleased( MouseEvent e ) { }
…
Example — Keyboard Input
«
«
«
´
}
…
public
bli void
id mouseClicked(
Cli k d( MouseEvent
M
E
t e ) {
² x = e.getX(); y = e.getY();
² s = "";
;
² repaint();
² e.consume(); }
public void paint( Graphics g ) {
² g.setColor( Color.gray );
² g.drawLine(
d
Li ( x, y, x, y-10
10 )
);
² g.drawLine( x, y, x+10, y );
² g.setCo
g.setColor(
o ( Co
Color.green
o .g ee );
² g.drawString( s, x, y ); }
Example — Threads
´
´
´
´
´
import java.applet.*;
i
import
t j
java.awt.*;
t *
import java.util.*;
import java.text.
java.text.*;
;
public class Clock extends Applet implements Runnable
{
« int width, height;
« Thread t = null;
« boolean threadSuspended;
« int hours=0, minutes=0, seconds=0;
« String timeString = "";
« public void init() {
² width = getSize().width; height =
getSize().height;
tSi () h i ht
² setBackground( Color.black ); }
Example — Threads
«
«
…
public
bli void
id start()
t t() {
² if ( t == null ) {
¹ t = new Thread( this );
¹ t.setPriority( Thread.MIN_PRIORITY );
¹ threadSuspended = false;
¹ t.start(); }
² else {
¹ if ( threadSuspended
th
dS
d d ) {
° threadSuspended = false;
« sy
synchronized(
c o
ed( t
this
s ) { notify();
ot y(); }
° } } }
² public void stop() { threadSuspended = true; }
²…
Example — Threads
«
«
…
public
bli void
id run()
() {
² try {
² while (true) {
¹ Calendar cal = Calendar.getInstance();
¹ hours = cal.get( Calendar.HOUR_OF_DAY );
¹ if ( hours > 12 ) hours -= 12;
¹ minutes = cal.get( Calendar.MINUTE );
¹ seconds
d = cal.get(
l
t( Calendar.SECOND
C l d
SECOND );
)
¹ SimpleDateFormat formatter = new
SimpleDateFormat( "hh:mm:ss",
Locale.getDefault() );
¹ Date date = cal.getTime();
¹ timeString
ti St i
= formatter.format(
f
tt
f
t( d
date
t )
);
²…
Example — Threads
«
…
«
if ( threadSuspended
th
dS
d d ) {
° synchronized( this ) {
« while ( threadSuspended ) { wait(); }
° } }
¹ repaint();
¹ t.sleep( 1000 );} }
² catch (InterruptedException e) { } }
void
id drawHand(
d
H d( d
double
bl angle,
l
i t radius,
int
di
G
Graphics
hi
g ) {
² angle -= 0.5 * Math.PI;
² int x = (int)( radius*Math.cos(angle) );
² int y = (int)( radius*Math.sin(angle) );
² g.drawLine( width/2,
/
height/2,
/
width/2
/ + x,
height/2 + y ); }
…
¹
«
Example — Threads
«
«
«
…
void drawWedge( double angle, int radius, Graphics g ) {
² angle -= 0.5 * Math.PI;
² int x = (int)( radius*Math.cos(angle) );
² int
i t y = (int)(
(i t)( radius*Math.sin(angle)
di * th i (
l ) )
);
² angle += 2*Math.PI/3;
² int x2 = (int)( 5*Math.cos(angle) );
² int y2 = (int)( 5*Math.sin(angle) );
² angle += 2*Math.PI/3;
² int x3 = (int)( 5*Math.cos(angle)
5*Math cos(angle) );
² int y3 = (int)( 5*Math.sin(angle) );
² g.drawLine( width/2+x2, height/2+y2, width/2 + x,
h i h /2 + y )
height/2
);
² g.drawLine( width/2+x3, height/2+y3, width/2 + x,
height/2 + y );
² g.drawLine( width/2+x2, height/2+y2, width/2 + x3,
height/2 + y3 ); }
…
Example — Threads
«
«
´
}
…
public void paint( Graphics g ) {
² g.setColor( Color.gray );
² drawWedge( 2*Math.PI * hours / 12, width/5, g );
² drawWedge( 2*Math.PI * minutes / 60, width/3, g );
² drawHand( 2*Math.PI * seconds / 60, width/2, g );
² g.setColor( Color.white );
² g.drawString( timeString, 10, height-10 ); }
REFERENCES
´
´
http://java.sun.com/docs/books/tutorial/deployme
h
//j
/d /b k /
i l/d l
nt/applet/index.html
http://www.dgp.toronto.edu/~mjmcguff/learn/java/