Download Savitch Java Ch. 1

Week 1
Introduction to Computers and
Java

Background information
» important regardless of programming language

Introduction to Java
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Computer Basics
Computer system: hardware + software
 Hardware: the physical components
 Software: the instructions that tell the
hardware what to do

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Common Hardware Components

Standard Hardware
Organization
» Central Processing Unit
» Interprets and executes the
instructions

(main & auxiliary)

(such as mouse and
keyboard)
Processor
(CPU)
Memory
» main & auxiliary
» holds data and instructions
Memory
Input
Devices
Processor (CPU)
Output
Devices
(such as video
display or printer)
Input device(s)
» mouse, keyboard, etc.

Output device(s)
» video display, printer, etc.

CPU and memory are
physically housed together
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Physical Organization



Keyboard
Monitor
Chassis
»
»
»
»
»
CPU
memory
disk drives
I/O connectors
etc.
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Running a Program
Program—a set of instructions for a computer to follow
Program
Data
(input for the program)
Computer
Output
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Many Types of Programs


User-created applications
Existing applications
»
»
»
»

word-processor/editor
web browser
compiler or assembler
etc.
Operating System
» DOS, Microsoft Windows, MacOS, Linux, UNIX,
etc.
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Various Types of User Interfaces

Command-line
» type in key words and letters
» DOS, Linux, and UNIX

Menu
» parts of DOS and Windows

GUI (Graphical User Interface)
» click on icon
» also called “event-driven”
» MacOS, Windows
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Programming Language
Hierarchy
High-Level Language (HLL)
Assembly Language
Machine Language
Hardware
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The highs and lows
of programming languages ...
High-Level Language (HLL)
» closest to natural
language
» words, numbers, and
math symbols
» not directly understood by
hardware
» “portable” source code
(hardware independent)
» Java, C, C++, COBOL,
FORTRAN, BASIC, Lisp,
Ada, etc.
Machine Language
(lowest level)
» least natural language for
humans, most natural
language for hardware
» just 0s and 1s
» directly understood by
hardware
» not portable (hardware
dependent)
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Assembly Language
(middle level)




a more or less human readable version of machine
language
words, abbreviations, letters and numbers replace 0s
and 1s
easily translated from human readable to machine
executable code
like machine code, not portable (hardware
dependent)
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Object-Oriented Programming: OOP





A design and programming technique
Some terminology:
» object - usually a person, place or thing (a noun)
» method - an action performed by an object (a verb)
» type or class - a category of similar objects (such as
automobiles)
Objects have both data and methods
Objects of the same class have the same data elements and
methods
Objects send and receive messages to invoke actions
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Example of an Object Class
Class: Automobile
Data Items:
»
»
»
»
»
»
»
»
manufacturer’s name
model name
year made
color
number of doors
size of engine
odometer miles
miles per gallon
Methods:
» Define data items
(specify manufacturer’s
name, model, year, etc.)
» Change a data item
(color, engine, etc.)
» Display data items
» Calculate cost
» Calculate mpg
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Inheritance

Inheritance—a way of organizing classes

Term comes from inheritance of traits like eye color,
hair color, and so on.

Classes with properties in common can be grouped
so that their common properties are only defined
once.
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An Inheritance Hierarchy
Vehicle
Automobile
Sedan
Motorcycle
Sports Car
School Bus
Bus
Luxury Bus
What properties does each vehicle inherit from the types
of vehicles above it in the diagram?
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Algorithms

Algorithm - a set of instructions (steps) for solving a
problem.
» must be precise
» must be complete

May be in a number of different formats
» natural language (such as English)
» a specific programming language
» a diagram, such as a flow chart
» pseudocode - a mix of natural and programming
language
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Example of an Algorithm
Algorithm that determines the total cost of a list of items:
1. Write the number 0 on the blackboard.
2. Do the following for each item on the list:
--Add the cost of the item to the number on the blackboard.
--Replace the old number on the board by this sum.
3. Announce that the answer is the number written on the
board
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Testing and Debugging

Even with careful programming, your
code could still contain errors and must
be thoroughly tested.
Bug—a mistake in a program
 Debugging—finding mistakes in a
program and (possibly) fixing them

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The Java Programming Language
History
 1991 - James Gosling, Sun Microsystems, Inc.
 originally a language for programming home appliances
 later (1994) used for World Wide Web applications (since
byte code can be downloaded and run without compiling it)
 eventually used as a general-purpose programming
language (for the same reason as above plus it is objectoriented)
 Why the name “Java”? Not sure - it may just be a name
that came during a coffee break and it had not been
copyrighted, yet.
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Applets vs. Java Applications

Applets
» Java programs intended to be downloaded via the Web and
run immediately
» “little applications”
» requires a web browser

Applications
» Java programs intended to be installed then run
» often larger applications

Slightly different programming for each, but both are
easy to do
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