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Introduction to Java Programming
CS 21a: Introduction to Computing I
Department of Information Systems
and Computer ScienceAteneo de Manila University
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.
L1: Intro JavaSlide 2
Programming
Recall that a program is defined as:a sequence of instructions for a computer
A large part (but not all) of CS 21a is about how to write programs in a programming language (Java)
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.
L1: Intro JavaSlide 3
The JavaProgramming Language
Java: an object-oriented programming language that is simple safe platform independent designed for the internet
Many universities use Java as the introductory programming language for beginning programmers Ateneo adopted Java for CS 21a in 1997
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.
L1: Intro JavaSlide 4
Java (a brief history) 1991
Sun Microsystems develops a language (based on C) for consumer electronic devices
1993 WWW explodes in popularity increased need for “dynamic” Web pages
1995 Sun formally announces Java for web use
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.
L1: Intro JavaSlide 5
Two types of Java programs:
Applications general-purpose programs standalone executed through the operating system
Applets programs meant for the WWW embedded in a Web page normally executed through a browser
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.
L1: Intro JavaSlide 6
Simple Java Application
File: Hello.java
// Hello World application
public class Hello
{
public static void main( String args[] )
{
System.out.println( “Hello world” );
}
}
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.
L1: Intro JavaSlide 7
The Programming Process
Create/EditProgram
CompileProgram
ExecuteProgram
Compile Errors? Run-Time Errors?
SourceProgram
ObjectProgram
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.
L1: Intro JavaSlide 8
Creation, Compilation, and Execution
Create Java programC:\> edit Hello.java Hello.java file is created
Compile using javac (compiler)C:\> javac Hello.java Hello.class file is produced
Execute using java (interpreter)C:\>java Hello requires a Hello.class file
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.
L1: Intro JavaSlide 9
Simple Java AppletFile: HelloAgain.java
import javax.swing.*;import java.awt.*;public class HelloAgain extends JApplet{ public void paint( Graphics g ) { g.drawString( “Hello”, 50, 50 ); }}
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.
L1: Intro JavaSlide 10
Executing Applets
After compiling the java program:
Embed an “applet tag” in an .html document that references the .class file
Open the .html document using a browser or the appletviewer
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.
L1: Intro JavaSlide 11
Sample .html Document
File: HA.html
<h1> My Sample Applet </h1><applet code=“HelloAgain.class” height=200
width=100></applet>
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.
L1: Intro JavaSlide 12
What is HTML?
Hypertext Markup Language Underlying language of Web pages A means of providing formatting
instructions for presenting content Text-based .html documents:
collection of content and controls (tags)
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.
L1: Intro JavaSlide 13
Java Program Structure
Java Program (optional) import declarations class declaration
Class class name should match its file name may extend an existing class
(such as JApplet) contains method/function declarations