1. CS413: Java Programming language Applications Applets
Conceived by Sun Microsystems
Benefits
Runs on any Java enabled Web Browser No installation or setup adjustments No need to scan for viruses Can create large graphics (charts, tables) on the fly No need to download large graphics Increase download speed
Security Features
Runtime examination: program is examined line-by-line for valid Java only code
Restricted Interactivity: Built-in restrictions on establishing connections to other computers The Java applet can only connect to the Internet location it came from
Restricted Access Rights: Built in restrictions on a program being able to read and write data
A program can only access the parts of a computer where it has received advance permission to access

2. CS413: Java
Usage samples Interaction with a user Calculate information of a web page Administer a quiz ‘Dress’ a web page Control animation on a web page Control GUI interfaces
Open System
Any hardware or software product that matches the published specifications
Published specifications establish a shared definition of how components must work together
Sun Microsystems has published detailed specifications for Java A program written in Java can run on any Java-enabled system with no adaptation required
Permits programs to be:
More widely distributed More easily easily used

3. CS413: Java Java Applet (Internet Web Page)
Manipulate words, numbers, and pictures
Create and control GUI interface
Display windows, buttons, and menus
User to point and click with a mouse to control actions
Information displayed in a variety of colours, styles, and sizes
Graphical User Interface (GUI)
Enables the user to do all of the above to make the web page/site easier and more interesting to use

4. CS413: Java
Java Applet
A mini program written Java and attached to a web page Fast to download
Enhance the web page display
Enable the user to interact with the web page
Enable the user to complete specific tasks
Manipulates data
Creates graphics

5. CS413: Java Programmer User Text file Extension of .java
Source Code anyname.java
Java compiler
Java compiler javac
Applet file ‘Bytecode’ anyname.class
Executable Java applet .class
HTML page
HTML page anyname.html
Java enabled browser anyname.html
HTML page Java translator anyname.html
User

6. CS413: Java Assembler Compiler
Creates a machine language executable file (program)
Programs written in Assembler language
Each Assembler language instruction generates one machine language instruction
Fast execution
Compiler
Programs written in higher level languages COBOL, PL1, RPG, FORTRAN
Each programming language instruction generates one or more machine language instructions

7. CS413: Java
Translator
DOES NOT create machine language executable file (program)
Limited instruction set (compared to Assembly and Compiler languages)
Slow processing Every instruction is read from the input file and processed individually 1. Instruction is read into the translator 2. Converted by the ‘Translator’ to 1 or more machine language instructions 3. Instruction is executed 4. Cycle starts again with next instruction
Slow processing due to
Loops
Decision blocks

8. Java creation/compile/execution (translation) Using DOS
CS413: Java
Java creation/compile/execution (translation) Using DOS
Create the Java code in a text editor
Save the file somename.java extension
Open a DOS window
Enter path command at the c:\windows> prompt path=c:\jdk1.2.2\bin
Change DOS directory to where the .java file is located
Enter javac somename.java To compile the Java code to a .class file
Fix any errors and re-compile (Step 6)
When no more errors - continue
Enter java somename To execute the compiled version

9. CS413: Java
Java creation/compile/execution (translation) Using Java Development Kit (JDK)

10. LAB I: Java program CS413: Java import java.applet.*;
import java.awt.*;
/**
This is a comment block */
public class HelloWorld extends Applet {
Label helloLabel = new Label(“Yo, you lookin’ at me?”);
public void init() {
setBackground(Color.yellow);
add(helloLabel); }

11. CS413: Java Java code in a Web page Basic HTML Document
Create an HTML document in a text editor Save as .htm or .html file
Insert the following Java code in the <body> area of the HTML file
<APPLET CODE= “somename.class” width=300 height = 50></APPLET>
Open the .htm/.html file in a browser
Basic HTML Document
<HTML>
<HEAD>
<TITLE></TITLE>
</HEAD>
<BODY>
</BODY>
</HTML>

12. Java Program Description
CS413: Java
Java Program Description
import java.applet.*; Reference a Java library of pre-written code * = make all library code members accessible
import java.awt.*; Reference a Java library of pre-written code * = make all library code members accessible
/** begin comment area
This is a comment block
*/ end comment area
public class HelloWorld extends Applet { public = the applet is accessible by outside programs class = defines this applet as a Java class HelloWorld = name of the Java class extends Applet = required for a Java class declaration
Label helloLabel = new Label(“Yo, you lookin’ at me?”); Label = Java code from the Java.awt library Display something on the screen helloLabel = programmer name of the Label new Label = Java definition creating the Label ( ….) = Text to be displayed on the screen

13. Java Program Description
CS413: Java
Java Program Description
public void init() {
Define what is to happen at applet initalization
setBackground(Color.yellow); Set the background color to yellow
add(helloLabel); Add the data from helloLabel to the graphic
} end of ‘public void’ method
} end of entire applet