Introduction to Java Programming

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Introduction toJava Programming

• Y. Daniel Liang

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Introduction

• What is a computer?
• Electronic devices that stores and process data
• Includes both hardware and software
• Hardware physical aspects that you can see
• Central Processing Unit (CPU)
• Memory (main memory)
• Storage Devices (hard disk, floppy disk, CDs,
  tapes)
• Input and Output Devices (monitors, keyboards,
  mice, printers)
• Communication Devices (modems and network
  interface cards)

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Hardware

• Central Processing Unit (CPU)
• Brain of a computer
• Retrieves instructions from memory and executes
  them
• 2 components
• control unit
• controls and coordinates the actions of the other
  components
• arithmetic/logic unit
• perform numeric operations (addition,
  subtraction, multiplication, division)
• Perform logic operations (comparison)
• Built on semiconductor chip with millions of
  transistors

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Hardware

• Memory (main memory)
• Data are encoded as a series of bits.
• Bit binary digit zero and one
• Stores data and program instructions for CPU to
  execute
• A memory unit is an ordered sequence of bytes,
  each holding 8 bits
• Encoding scheme ASCII

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Hardware

• Memory (main memory)
• A program and its data must be brought to memory
  before they can be executed
• The content of memory is lost when new infor is
  placed in it.
• Each byte has a unique address, used to locate
  the byte.
• Can be accessed in any order, thus is called RAM
  (Random-access memory)
• 1 Megabyte (MB) is about 1 million bytes.
• Also built on silicon semiconductor ships
  containing thousands of transistors, but less
  complicated.
• Memory is volatile, the content is lost when the
  power is turned off.

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Hardware

• Storage Devices (hard disk, floppy disk, CDs,
  tapes)
• Programs and data are stored permanently on
  storage devices and moved to memory when computer
  actually uses them.
• 4 main types of storage devices
• Disk drives (hard disks, floppy disks)
• CD drives (CD-R, CD-RW, DVD). DVD stands for
  Digital versatile disc.
• Tape drives
• USB flash drives

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Hardware

• Input and Output Devices (monitors, keyboards,
  mice, printers)
• Allows user to communicate with the computer
• Common input devices keyboards, mice
• Common output devices monitors, printers.

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Hardware

• Communication Devices (modems and network
  interface cards)
• To create network of computers

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Software

• Software/computer program
• invisible instructions that control the hardware
  and make it perform specific tasks.
• Tell computer what to do in computer/machine
  language

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Software

• Computer languages
• Machine language
• Assembly language
• High level language

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Software

• Machine language
• a set of primitive instructions built into every
  computer
• Different for different types of computers.
• The instructions are in the form of binary code,
  e.g. to add 2 numbers (very tedious)
• 1101101010011010

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Software

• Assembly language
• Low-level programming language which uses
  mnemonic to represent machine-language
  instructions
• E.g. ADDF3 R1, R2, R3
• Assembly code need to be converted into machine
  code by using an assembler
• Assembly program
• is platform dependent
• Combination of mnemonic and machine instruction

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Software

• High-level language
• English-like and easy to learn and program.
• E.g.
• Area 5 5 3.1415
• COBOL, FORTRAN, BASIC, Pascal, Ada, C, Visual
  Basic, Delphi, C, C, Java
• Source program is compiled into machine code by a
  compiler and linked to supporting library code by
  a linker to form an executable file. Fig. 1.4

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Software

• High-level language (continue)
• Can port/move a source program to any machine
  with appropriate compilers but the source program
  must be recompiled
• Java program, compiled it once into intermediate
  machine code known as bytecode. Bring the
  bytecode to any computer with a JVM (Java Virtual
  Machine). JVM interprets the bytecode into the
  machine codes and execute them.

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An overview of the java development process.
Source http//java.sun.com/docs/books/tutorial/ge
tStarted/intro/definition.html
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Through the Java VM, the same application is
capable of running on multiple platforms.
Source http//java.sun.com/docs/books/tutorial/ge
tStarted/intro/definition.html
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Software

• Compiling versus interpreting
• Compiling translates the high-level code into a
  target language code as a single unit
• Interpreting translates the individual steps in
  the high level code one at a time. Each step is
  execute immediately after it is translated.

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Software

• Operating system (OS)
• Software that controls and manages the systems
• Fig. 1.6, page 36.
• E.g. Windows (98, NT, XP, ME), MacOS, Linux etc.
• Major tasks
• Controlling and monitoring system activities
  (security, input, output, file directories, make
  sure programs running together do not interfere
  with each other)
• Allocating and assigning system resources to
  program
• Scheduling operations
• Multiprogramming multiple programs to run
  simultaneously by sharing CPU
• Multithreading allows concurrency within a
  program it subunits can run at the same time
  (e.g. editing and saving at the same time)
• Multiprocessing/parallel processing use 2 or
  more processors together to perform a task.

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What Is Java?

• History
• Characteristics of Java

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History

• James Gosling
• Oak 1991, for embedded consumer electronic
  appliances
• Renamed Java, 1995, for developing Internet
  applications
• HotJava
• The first Java-enabled Web browser
• Java applets java programs that run from a Web
  browser
• http//javaboutique.internet.com/movingtree/

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Characteristics of Java

• Java is simple
• Java is object-oriented
• Java is distributed
• Java is interpreted
• Java is robust
• Java is secure
• Java is architecture-neutral
• Java is portable
• Javas performance
• Java is multithreaded
• Java is dynamic

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Java IDE Tools

• Inprise JBuilder
• Microsoft Visual J
• Symantec Café
• Forte by Sun MicroSystems
• IBM Visual Age for Java
• NetBeans 6.0 (free, open-source IDE, runs on
  Windows, Linux, Solaris, and the MacOS)
• JCreator LE 4.0 (free) by Xinox Software

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Java Language Specification, API, JDK and IDE

• Java Language Specification
• Technical definition of the language which
  includes the syntax and semantics of the Java
  Programming language (java.sun.com/docs/books/jls)
  
• API
• Contains predefined classes and interfaces for
  developing Java programs.
• 3 editions of Java API
• J2SE - version Java SE 6.0 (jdk1.6.0_02)
• J2EE
• J2ME

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Java Language Specification, API, JDK and IDE

• JDK
• A set of programs for developing and testing Java
  program, each of which is invoked from a command
  line.
• IDE (integrated development environment)
• Software that provides integrated development
  environment (editing, compiling, building,
  debugging and online help) for rapidly developing
  Java program

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Getting Started with Java Programming

• A Simple Java Application
• Compiling Programs
• Executing Applications

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A Simple Application

• Example 1.1
• //This application program prints Welcome
• //to Java!
• public class Welcome
• public static void main(String args)
• System.out.println("Welcome to Java!")

Run
Source
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Creating, compiling and executing a Java Programs

• Fig. 1.11, page 44.

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Compiling Programs

• On command line
• javac file.java

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Executing Applications

• On command line
• java classname

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Example

• javac Welcome.java
• java Welcome
• output...

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Anatomy of a Java program

• Comments
• Reserved words
• Modifier
• Statement
• Block
• Class
• Method
• The main method

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Anatomy of a Java program

• Comments
• Documents the program for understanding purpose
• Ignored by compiler
• //
• / /
• Reserved words or keywords
• Words that have specific meaning to the compiler
  and cannot be used for other purposes in the
  program
• E.g public, static, class, void

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Anatomy of a Java program

• Modifier
• Certain reserved words are modifiers that specify
  the properties of the data, methods and class and
  how they can be used.
• E.g public, private, static, final, abstract,
  protected.
• Statement
• Represents an action or a sequence of actions
• Ends with semicolon ()
• Block
• Groups the components of the program
• Begins with opening brace and ends with a
  closing brace
• Class block, method block

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Anatomy of a Java program

• Class
• Program is defined by using one or more class
• Will be covered in more details later.
• Method
• A collection of statements that perform a
  sequence of operations.
• Can be used without fully understanding how it
  works.
• Invoke by calling the method name with the
  requirement argument
• The main method
• A special method where the program execution
  begins.
• JVM invokes the main method to execute an
  application.

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Summary