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Transcript 
User Interface Programming
In Java
Part 1 – Introduction
Marc Abrams
Virginia Tech CS Dept
courses.cs.vt.edu/wwwtut/
9/21/99
www.cs.vt.edu/wwtut/
1
History



Evolved from Sun project to write code for
consumer electronics
Gosling and colleagues began
adding/subtracting C++ features
In 1993, developers realized Java’s potential
for Web.

9/21/99
Wrote HotJava browser, with HTML support for
applets.
www.cs.vt.edu/wwtut/
2
Java 1 Features (1)

Simplicity
Garbage collection, single inheritance, less C/C++.
But… you must learn a boatload of classes!


Object-oriented
Distributed



network communication classes
Architecture-neutral
Interpreted

9/21/99
portable
www.cs.vt.edu/wwtut/
3
Java 1 Features (2)

Robust (?)


Secure




eliminates common bugs: pointers, arrays
more so with Java 2
Multithreaded
No type system violations
Dynamic

9/21/99
dynamically load classes over network
www.cs.vt.edu/wwtut/
4
What’s New in Java 2

Enhanced Security

Fine-grained security manager
(e.g., grant write access only to a particular file)






Digitally signed apps and applets
Swing UI components
Java 2D API
Accessibility API
Drag & drop to/from non-Java apps, between Java
apps, w/in one Java app
Custom cursors
9/21/99
www.cs.vt.edu/wwtut/
5
What’s New in Java 2





Navigation with keyboard only (w/o mouse)
“Collections” – container classes that generalize
Vector, Hashtable, Array. Like C++’s Standard
Template Library.
Input Methods for Japanese, Chinese, or Korean
text
Package-level version numbers
Enhancements to serialization, RMI, JavaBeans,
garbage collection, Java Native Interface, JDBC,
9/21/99
www.cs.vt.edu/wwtut/
6
What’s New in Java 2



Java Sound API Engine to play back WAV,
AIFF, …
Java IDL allows CORBA objects to be written
in Java
Performance improvements
See java.sun.com/products/jdk/1.2/docs/relnotes/features.html for more info.
9/21/99
www.cs.vt.edu/wwtut/
7
Where examples come from…
Java in a Nutshell, 2nd Edition
www.ora.com/catalog/javanut2/
Examples:
www.ora.com/catalog/javanut2/examples/
However, this book only covers Java 1.1.
9/21/99
www.cs.vt.edu/wwtut/
8
Try this now…



Construct an HTML page.
Page contains a Java applet.
Java applet prints “hello world”.
(Click here to run example.)
9/21/99
www.cs.vt.edu/wwtut/
9
//
//
//
//
//
//
This example is from the book "Java in a Nutshell, Second Edition".
Written by David Flanagan. Copyright (c) 1997 O'Reilly & Associates.
You may distribute this source code for non-commercial purposes only.
You may study, modify, and use this example for any purpose, as long as
this notice is retained. Note that this example is provided "as is",
WITHOUT WARRANTY of any kind either expressed or implied.
Solution (Ex. 6-1)
import java.applet.*;
import java.awt.*;
// Don't forget this import statement!
// Or this one for the graphics!
public class FirstApplet extends Applet {
// This method displays the applet.
// The Graphics class is how you do all drawing in Java.
public void paint(Graphics g) {
g.drawString("Hello World", 25, 50);
}
}
9/21/99
www.cs.vt.edu/wwtut/
10
Analysis of Code

Invoked by HTML page:
<HTML>
<HEAD>
<TITLE>My First Applet</TITLE>
</HEAD>
<BODY>
This is the world's simplest applet.
<P>
<APPLET code="FirstApplet.class" width=150 height=100>
</APPLET>
</BODY>
</HTML>
9/21/99
www.cs.vt.edu/wwtut/
11
Analysis of Code





No

main() function

Function declarations
import java.applet.*;
import java.awt.*;
Only class declarations
Inherits from pre-defined
class in package
Package names are
(theoretically) globally unique
Default: names visible only
within package
9/21/99
public class FirstApplet
extends Applet {
public void paint(Graphics g)
{
g.drawString(
"Hello World", 25, 50);
}
}
www.cs.vt.edu/wwtut/
12
Analysis of Code

To compile:
javac FirstApplet.java

Compile creates
bytecode:
FirstApplet.class
9/21/99
import java.applet.*;
import java.awt.*;
public class FirstApplet
extends Applet {
public void paint(Graphics g)
{
g.drawString(
"Hello World", 25, 50);
}
}
www.cs.vt.edu/wwtut/
13
What is java.applet?
Object
Java.lang
 Component
Java.awt
 Container
 Panel
 Applet Java.applet
9/21/99
import java.applet.*;
import java.awt.*;
public class FirstApplet
extends Applet {
public void paint(Graphics g)
g.drawString(
"Hello World", 25, 50);
}
}
www.cs.vt.edu/wwtut/
14
What is java.applet?
public class Applet extends Panel
{
…
public String getAppletInfo();
public String getParameter(
String name);
public void init(); //empty
public void start(); //empty
public void stop(); //empty
}
9/21/99
import java.applet.*;
import java.awt.*;
public class FirstApplet
extends Applet {
public void paint(Graphics g)
g.drawString(
"Hello World", 25, 50);
}
}
www.cs.vt.edu/wwtut/
15
Where is paint() defined?
(It’s not in applet!)
Object
Java.lang
 Component
Java.awt
 Container
 Panel
 Applet Java.applet
9/21/99
import java.applet.*;
import java.awt.*;
public class FirstApplet
extends Applet {
public void paint(Graphics g) {
g.drawString(
"Hello World", 25, 50);
}
}
www.cs.vt.edu/wwtut/
16
paint() is defined in
java.awt.Component
Object
Java.lang
 Component
Java.awt
 Container
 Panel
 Applet Java.applet
public abstract class Component
extends Object
{
…
public void paint(Graphics g);
//empty
}
9/21/99
import java.applet.*;
import java.awt.*;
public class FirstApplet
extends Applet {
public void paint(Graphics g) {
g.drawString(
"Hello World", 25, 50);
}
}
www.cs.vt.edu/wwtut/
17
What is java.awt.graphics?
Object
 Graphics
Java.lang
Java.awt
public class FirstApplet
extends Applet {
public void paint(Graphics g) {
g.drawString(
"Hello World", 25, 50);
} }
public abstract
class Graphics extends Object
{
…
public abstract void drawLine(int x1, int y1, int x2,int y2);
public abstract void drawOval(int x, int y, int w, int h);
public void drawString(String, int x, int y);
public void fillOval(int x, int y, int w, int h);
public void setColor(Color c);
public void setFont(Font c);
}
9/21/99
www.cs.vt.edu/wwtut/
18
What does entire java.awt
look like?

Show diagram on transparency
9/21/99
www.cs.vt.edu/wwtut/
19
Example 2… Variation on Hello
Word
9/21/99
www.cs.vt.edu/wwtut/
20
//
//
//
//
//
//
This example is from the book "Java in a Nutshell, Second Edition".
Written by David Flanagan. Copyright (c) 1997 O'Reilly & Associates.
You may distribute this source code for non-commercial purposes only.
You may study, modify, and use this example for any purpose, as long as
this notice is retained. Note that this example is provided "as is",
WITHOUT WARRANTY of any kind either expressed or implied.
Code
public void paint(Graphics g) {
// The pink oval
g.setColor(Color.pink);
g.fillOval(10, 10, 330, 100);
import java.applet.*;
import java.awt.*;
// Red outline. Simulate
// 4-pixel wide line
g.setColor(Color.red);
g.drawOval(10,10, 330, 100);
g.drawOval(9, 9, 332, 102);
g.drawOval(8, 8, 334, 104);
g.drawOval(7, 7, 336, 106);
public class SecondApplet extends
Applet {
static final String message =
"Hello World";
private Font font;
// The text
g.setColor(Color.black);
g.setFont(font);
g.drawString(message, 40,
75);
}
public void init() {
font = new Font("Helvetica",
Font.BOLD, 48);
}
}
9/21/99
www.cs.vt.edu/wwtut/
21
Analysis of Code

String



import java.applet.*;
import java.awt.*;
is a class, not char array
each char is 16-bit unicode
Font, Color are classes
9/21/99
public class SecondApplet extends
Applet {
static final String message =
"Hello World";
private Font font;
public void init() {
font = new Font("Helvetica",
Font.BOLD, 48);
}
public void paint(Graphics g) {
// The pink oval
g.setColor( Color.pink );
www.cs.vt.edu/wwtut/
22
What is java.awt.Color?
Object
 Color
Java.lang
Java.awt
public final class Color extends Object {
public Color(int r, int g, int b);
public Color(int rgb);
public Color(float r, float g, float b);
..
public final static Color pink;
}
9/21/99
g.setColor( Color.pink );
www.cs.vt.edu/wwtut/
23
What is java.awt.Font?
Object
 Font
Java.lang
Java.awt
public class Font extends Object {
public Font(String name, int style, int size);
public final static int BOLD;
// or ITALIC, PLAIN
...
}
font = new Font("Helvetica", Font.BOLD, 48);
9/21/99
www.cs.vt.edu/wwtut/
24
Recall java.awt.graphics…
Object
 Graphics
Java.lang
Java.awt
g.setColor(Color.pink);
g.fillOval(10, 10, 330, 100);
...
g.setColor(Color.red);
g.drawOval(10,10, 330, 100);
...
g.setFont(font);
public abstract
class Graphics extends Object
{
…
public abstract void drawLine(int x1, int y1, int x2,int y2);
public abstract void drawOval(int x, int y, int w, int h);
public void drawString(String, int x, int y);
public void fillOval(int x, int y, int w, int h);
public void setColor(Color c);
public void setFont(Font c);
}
9/21/99
www.cs.vt.edu/wwtut/
25
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