Embed Size (px)
Citation preview
Program Design With Methods And Graphics / Chapter 4
1
Abstract Window Toolkit
Program Design With Methods And Graphics / Chapter 4
2
Abstract Window Toolkit
• class library – graphics
• lines
• rectangles
• circles
– GUI• text boxes
• labels
• command buttons
Program Design With Methods And Graphics / Chapter 4
3
Java Application
– javac SomeApp.java– java SomeApp
byte codejavacjava source
machine codeJVM
byte code
compiling
executing
Program Design With Methods And Graphics / Chapter 4
4
Java Application
• execution starts with main
public static void main(String args[] ) { … }
Program Design With Methods And Graphics / Chapter 4
5
Java Applet
– javac SomeApplet.java– appletviewer SomeApplet.html
byte codejavacjava source
machine codeappletviewerhtml source
compiling
executing
Program Design With Methods And Graphics / Chapter 4
6
Java Applet
• execution starts with the browser / appletviewer– browser / appletviewer loads the .class file
Program Design With Methods And Graphics / Chapter 4
7
Appletviewer
• executes applet
• utility to test applets
• included with J2SDK
Program Design With Methods And Graphics / Chapter 4
8
Java Applet
public class Intersection extends Applet { …}
class name
keyword
base class
class Intersection inherits from base class Applet
Program Design With Methods And Graphics / Chapter 4
9
Java Appletjava applet has the following methods:
public void init()
public void start()
public void paint(Graphics g)
public void stop()
public void destroy()
Program Design With Methods And Graphics / Chapter 4
10
Java Applet
public void init()
•initializes the applet
•first method called by the browser or appletviewer
Program Design With Methods And Graphics / Chapter 4
11
Java Applet
public void paint(Graphics g)
•after init()
•refreshing the browser
Program Design With Methods And Graphics / Chapter 4
12
HyperText Markup Language (HTML)
<html>
<applet code =“class name.class” width=width height=height>
</applet>
</html>
Class name.html:
name of class width of display area
width of display area
Program Design With Methods And Graphics / Chapter 4
13
Java Applet
• className.html
• className.java
• className.class
the following must exist before executing an applet:
Program Design With Methods And Graphics / Chapter 4
14
Intersection Example(Intersection.java)
import java.awt.*;
import java.applet.Applet;
public class Intersection extends Applet{
public void paint(Graphics g){
//draws line from (0,0) to (300,200)
g.setColor(Color.black);
g.drawLine( 0, 0, 300, 200);
//draws line from (300, 0) to (0, 200)
g.setColor(Color.blue);
g.drawLine( 300, 0, 0, 200);
}
}
}
Program Design With Methods And Graphics / Chapter 4
15
Graphics
• setColor()
• drawLine()
• drawRect()
• drawString()
Program Design With Methods And Graphics / Chapter 4
16
setColor
• g.setColor(Color.black);– where g is the object
sets color
Program Design With Methods And Graphics / Chapter 4
17
drawLine()
•draws a line
g.drawLine(
);
start point x-coordinate,
end point x-coordinate,
start point y-coordinate,
end point y-coordinate
Program Design With Methods And Graphics / Chapter 4
18
drawLine()
g.drawLine( 0, 0, 300, 200);
starting point end point
•method name
•draws a line
Program Design With Methods And Graphics / Chapter 4
19
drawRect()•draws a rectangle based on its coordinates
object.drawRect(
upper left x-coordinate,
width of rectangle,
upper left y-coordinate,
height of rectangle,
);
•width and height of rectangle should be non negative values
Program Design With Methods And Graphics / Chapter 4
20
drawRect()
g.drawRect(15, 10, 270, 20);
upper left x-coordinate, upper left y-coordinate,
width of rectangle, height of rectangle,
Program Design With Methods And Graphics / Chapter 4
21
drawString()
draws a string at the specified location
object.drawString(“string”, x-coordinate, y-coordinate)
syntax
string to print
•coordinates (or position) at which the string is drawn
•coordinates are measured from the upper left corner of applet
Program Design With Methods And Graphics / Chapter 4
22
drawString
object.drawString(“The sum is” + sum , 25, 25);
string to print x-coordinate y-coordinate
Program Design With Methods And Graphics / Chapter 4
23
Additional Graphics
• See page 163
