CSCE 145: Algorithmic Design IChapter 1Intro to Computers and Java

Muhammad Nazmus Sakib

Computer Basics

•Section 1.1

Computer Systems

•Hardware▫The Physical Machine

•Software▫Set of programs

Set of instructions

Hardware and Memory

•Central Processing Unit (CPU)▫Also known as the Processor▫Device that performs the instructions in a

program▫Example

Intel Core i7

Hardware and Memory

•Memory▫Holds data for the computer to process▫Two forms

Main Memory Volatile Example - RAM

Auxiliary Memory Non-volatile Example – Hard drive

Bits, Bytes & Address•Bit = Binary Digit (0,1)•Byte = groups of bits

▫1 Byte = 8 Bits▫Byte is the smallest addressable unit of

memory•Address

▫Main memory consists of a long list of numbered bytes

▫The number of a byte in memory is called an Address

Memory Locations

•1 byte is not large enough to store all kinds of data

•Data can be stored in several adjacent bytes

•These adjacent bytes are considered a single Memory Location

•Address of the Memory Location▫Address of the first byte

Main Memory

Files & Directories

•File▫A group of bytes stored in auxiliary

memory•Directory

▫Also known as Folder▫Contains groups of files

Programs

•A set of instructions

Operating Systems

•A program that supervises a computer’s operation

•Examples▫Windows XP/7/8▫UNIX▫Linux, Ubuntu▫Mac OS X

Programming Languages

•High Level Languages▫Java, C, C++, C#, Visual Basic, Python

•Low Level Languages▫Assembly Language▫Machine Language

Compilers

•A Translator•Translates from High Level Language to

Low Level Language•Source code -> Object Code•Compile Once, Execute Often

Interpreters

•Translator + Executor•Alternates between translation &

execution•Translates every time•Interpreted programs are slower than

compiled ones

Java Bytecode

•An intermediate language for Java•A compiler translated Java code into

Bytecode•Java Virtual Machine (JVM)

▫Translator to translate & execute Java Bytecode

•Bytecode runs in any computer that has JVM▫Portability

Compiling & Running

Class Loader

•Java program consists of Classes▫A piece of code▫Generally reside in one file

•Class loader connects the Classes▫Similar to a Linker

A Sip of Java

•Section 1.2

History of Java

•Started in 1991•James Gosling and his team

▫Sun Microsystems

Applications & Applets

•Applications▫Regular programs▫Runs in your computer

•Applets▫Little applications▫Runs in your web browser▫Sent over the Internet

Programming Basics

•Section 1.3

Object-Oriented Programming

•Objects▫Attributes▫States▫Behaviors

•Methods▫Captures the behavior

•Classes▫Blueprint for Objects

Object-Oriented Programming

•Encapsulation▫Information Hiding

•Polymorphism▫Many forms▫Example – “Go play your favorite sport”

•Inheritance▫Way of organizing Classes

Inheritance

Algorithms

•Like a Recipe!•A set of directions for solving a problem•Often written in Pseudocode

▫Combination of English & Programming Language

Pseudocode Example

•Algorithm to compute the total cost of a list of items▫Write the number o on the whiteboard.▫For each item on the list

Add the cost of the item to the number on the whiteboard

Replace the number on the whiteboard with the result of this addition.

▫Announce that the answer is the number written on the whiteboard.

Testing & Debugging

•Bug▫A mistake in a program

•Debugging▫Process of eliminating mistakes

•Syntax error▫Grammatical mistakes

•Run-time error▫Error during execution

•Logic error▫Conceptual mistakes in algorithm

Software Reuse

•Java Class Library▫Java API

•Example▫System.out.println