Chapter 1: Introduction

1
Xavier University Computer Center Sun
Microsystems, Philippines
Java sa Eskwela (JsE) Program
2
Chapter 1
Introduction to Java
3
Chapter 1

• Outline
• History of Java
• Java Class Libraries
• Basics of a Typical Java Environment

4
Objectives

• To become familiar with how Java evolved
• To understand the Java program development
  environment

5
Introduction

• Java
• based on C and C
• developed by a team led by Patrick Naughton, Mike
  Sheridan, and James Gosling (the Green Project)
• developed in early 1991 for intelligent consumer
  electronic devices
• Market did not develop, project in danger of
  being cancelled

6
Introduction

• Java
• Internet exploded in 1993, saved project
• Used Java to create web pages with dynamic
  content
• Java formally announced in 1995
• Now used to create web pages with interactive
  content, enhance web servers, applications for
  consumer devices (pagers, cell phones)

7
Introduction

• both compiled and interpreted language
• vs. C/C source is refined to native
  instructions for a particular model of processor
• compiled to universal format (byte-code) which is
  a set of instructions for a virtual machine

8
Introduction

• Java Byte-code
• compiled Java Source
• also called J-code
• executed by a Java run-time interpreter

9
Source Code Class temp ..
Java Runtime
Byte-code
PC
Mac
UNIX
10
Introduction

• Java Programs
• consist of pieces called classes
• classes contain methods, which perform tasks
• Class libraries
• also known as Java API (Applications Programming
  Interface)
• rich collection of predefined classes, which you
  can use

11
Introduction

• Two parts to learning Java
• Learning the language itself, so you can create
  your own classes
• Learning how to use the existing classes in the
  libraries

12
Introduction

• Five Phases
• Edit
• Use an editor to type Java program (e.g. vi or
  emacs, notepad, Jbuilder, JCreator)
• .java extension
• Compile
• Translates program into byte-codes, understood by
  Java interpreter
• javac command javac myProgram.java
• Creates .class file, containing byte-codes
  (myProgram.class)

13
Introduction

• Five Phases (continued)
• Loading
• class loader transfers .class file into memory
• Applications run on user's machine
• Applets loaded into Web browser, temporary
• classes loaded and executed by interpreter with
  java command
• java Welcome
• HTML documents can refer to Java Applets, which
  are loaded into web browsers.

14
Introduction

• Five Phases (continued)
• Verify
• Byte-code verifier makes sure byte-codes are
  valid and do not violate security
• Java must be secure Java programs transferred
  over networks, possible to damage files (viruses)
• Execute
• computer (controlled by CPU) interprets program
  one byte-code at a time
• performs actions specified in program

15
Introduction
Program is created in the editor and stored on
disk.
P1
Editor
Sec. Memory
Compiler creates byte-codes and stores them on
disk.
P2
Compiler
Class Loader
P3
Class loader puts byte-codes in memory.
Sec. Memory
Primary Memory
16
Introduction
P4
Verifier
Byte-code verifier confirms that all byte-codes
are valid and do not violate Javas security
restrictions.
Primary Memory
Interpreter reads bytecodes and translates them
into a language that the computer can
understand, possibly storing data values as
the program executes.
P5
Interpreter