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Introduction to Java Programming

Introduction to Java Programming. CS 21a: Introduction to Computing I First Semester, 2013-2014. 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).

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Introduction to Java Programming

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  1. Introduction to Java Programming CS 21a: Introduction to Computing I First Semester, 2013-2014

  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)

  3. The Java Programming 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

  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

  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

  6. Simple Java Application File: Hello.java // Hello World application public class Hello { public static void main( String args[] ) { System.out.println( "Hello world" ); } }

  7. The Programming Process Compile Errors? Run-Time Errors? Create/Edit Program Compile Program Execute Program Source Program Object Program

  8. Creation, Compilation, and Execution • Create Java program C:\> 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

  9. Simple Java Applet File: HelloAgain.java import javax.swing.*; import java.awt.*; public class HelloAgain extends JApplet { public void paint( Graphics g ) { g.drawString( "Hello", 50, 50 ); } }

  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

  11. Sample .html Document File: HA.html <h1> My Sample Applet </h1> <applet code="HelloAgain.class" height=200 width=100> </applet>

  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)

  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

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