Chapter 1 Computers, Programs, and Java

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Chapter 1Computers, Programs, and Java
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Computer Science

• Why should anyone who doesnt want to be a
  computer scientist learn about computer science?
• Manipulation is done with a computer
• Media
• Business data
• Scientific data
• If you can only manipulate data with software
  that someone else created, you are limiting your
  ability to communicate.

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Hardware
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Software

• Software are the instructions that tell the
  hardware what to do.
• A set of software instructions that tells the
  computer what to do is called a computer program.
  
• A program is like a recipe
• There are different types of programs that make
  up a computer.

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Operating Systems

• An operating system, or OS, is the glue that
  binds the hardware to the application software.
• An operating system is a collection of computer
  programs dedicated to managing the resources of
  the system.
• What are some tasks the operating system manages?

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Machine Language

• All of the hardware components in a computer
  system, including the CPU, operate on a language
  made up of binary numbers
• Binary numbers are made up of only 2 digits - 0
  and 1.
• A CPU does not understand any other language.
• Every instruction is eventually translated into
  machine language.

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Assembly Language

• Assembly language is one step up from machine
  language.
• Assembly language employs alphabetic
  abbreviations called mnemonics.
• For instance, the mnemonic for addition is ADD,
  the mnemonic for move is MOV, and so forth.

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High-level language

• A high-level language consists of instructions,
  or statements, that are closer to English and
  common mathematical notation.
• When programming in a high-level language, you do
  not have to concern yourself with the specific
  machine language of the CPU.

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Structured Languages

• A structured language allows complex problems to
  be solved using a modular, top/down, approach.
• C is a structured programming language

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Object-Oriented programming (OOP)

• An object-oriented language allows complex
  problems to be solved using more natural objects
  that model the way we humans think about things
  in terms of attributes and behavior.
• C and Java are object-oriented programming
  languages

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A Quick Language Comparison Feature C C Jav
a
Object-Oriented No Yes Yes Easy
GUIs No No Yes Portable No No Yes Internet
Programming No No Yes Easy Multitasking
No No Yes Easy Database Connectivity No No Yes
Built-In Security No No Yes Simplicity No No
Yes High Speed Execution Yes Yes No Low Level
Coding Yes Yes No Widely Accepted Yes Yes Yes
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Structured vs. Object-Oriented Languages

• The C language is a structured language that
  allows complex problems to be solved using a
  modular, top/down, approach.
• The Java language is an object-oriented language
  that allows complex problems to be solved in
  terms of their attributes and behaviors, much
  like we humans view the world.

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Java

• In Java, you can write many different kinds of
  programs, including applications, applets,
  servlets, EJBs, and JavaBeans.
• Java applications are designed to be run on a
  computer just like any other computer program
  written in any other language.
• Java applets are programs designed only to be run
  over the Internet using a Web browser.

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Why Java?

• Object-oriented
• Portable compile once, deploy many
• Growing in popularity
• Cheap - free
• For our class
• Simpler than C
• A real programming language, not just scripting
• Once you know Java you can pick up any other
  language easily

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Creating a Program

• Even when programming in a high level language,
  the system must still translate your instructions
  into machine language.
• High level programming languages use either a
  compiler or an interpreter to translate the
  instructions into machine code.

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Compiler

• A compiler is a program that takes a high-level
  language program and translates the entire
  program into machine code all at one time.
• All instructions are compiled before any are
  executed by the CPU.

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Interpreter

• An interpreter translates and executes one
  high-level instruction at a time.
• Once a given instruction has been executed, then
  it translates and executes the next, and so on.

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Java Programs

• Java is unique in that it uses a compiler and an
  interpreter
• Type your program into an editor
• Save it in a file with a .java extension source
  code
• Invoke the Java compiler to translate the source
  code into Java bytecode (.class file)
• Bytecode is similar to machine language but not
  associated to any specific CPU
• Any computer with a Java Virtual Machine (JVM)
  has a Java interpreter
• Java interpreter translates the generic bytecode
  into machine language instructions specific to
  the CPU

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Language Translation

• A source program is the one that you write in the
  Java language and that always has a file
  extension of .java.
• An object program is the binary byte-code program
  generated by the Java compiler, which always has
  a file extension of .class.

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Language Translation

• The .class file generated by the Java compiler
  contains bytecode
• low-level code similar to machine language
• generic and not specific to any particular CPU.
• The Java Virtual Machine (JVM) translates the
  generic bytecode into machine language
• A computer must have a JVM to run the Java
  program.

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Java Translation
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Java Programs

• Why does Java use both a compiler and
  interpreter?
• What are the pros and cons of this?