8/11/2019 Programming Fundamentals Basics

1/2

Outline

Topics

Computer basics

Programming languages Simple Java program and method

Writing comments

Fun fact

The original name for Java is oak because of a big

oak tree that grew outside the developer's window. It

was eventually changed to Java

What is a Computer?

An electronic device that stores and

processes data

Hardware

Software

CPU

e.g., Disk, CD,

and Tape

Input

Devices

e.g., Keyboard,

Mouse

e.g., Monitor,

Printer

Communication

Devices

e.g., Modem, and

NIC

Storage

Devices MemoryOutput

Devices

Bus

How Data is Stored?

Various kinds of data

Numbers

Characters

Strings

A byte is the minimumstorage unit

E.g. J is represented by

01001010 in one byte

E.g. small number suchas 3 can be stored in a

single byte

.

.

.

2000

2001

2002

2003

2004

.

.

.

01001010

01100001

01110110

01100001

00000011

Memory contentMemory address

Encoding for character J

Encoding for character a

Encoding for character v

Encoding for character a

Encoding for number 3

Machine Languages

System of instructions and data directly

understandable by a computer's central

processing unit

Example:100011 00011 01000 00000 00001 000100

000010 00000 00000 00000 10000 000001

000000 00001 00010 00110 00000 100000

Every CPU model has its own machine

code, or instruction set, although there is

considerable overlap between them

Assembly Languages

Human-readable notation for the machine language that

a specific computer architecture uses representingelementary computer operations (translated via

assemblers)

Example:load hourlyRate

mul workHours

store salary

MUL R1, R2, R3

Assembly Source File

Assembler 1101101010011010

Machine Code File

High-level Languages

Higher level of abstraction from machine language

Codes similar to everyday English

Use mathematical notations (translated via compilers)

Example:

salary = hourlyRate * workHours

Make complex programming simpler

CompilerSource File Machine-languageFile

Linker Executable File

Library Code

http://en.wikipedia.org/wiki/James_Goslinghttp://en.wikipedia.org/wiki/James_Goslinghttp://en.wikipedia.org/wiki/James_Gosling

8/11/2019 Programming Fundamentals Basics

2/2

A Simple Java Program

//This program prints Welcome to Java!

public class Welcome {public static void main(String[] args) {

System.out.println("Welcome to Java!");

}

}

print a message to theconsole

The main method

program statement

Welcome.java

Creating, Compiling, and Running Programs

Source Code

Create/Modify Source Code

Compile Source Code

i.e., javac Welcome.java

Bytecode

Run Byteode

i.e., java Welcome

Result

If compilation errors

If runtime errors or incorrect result

public class Welcome {public static void main(String[] args) {

System.out.println("Welcome to Java!");}

}

Method Welcome()

0 aload_0

Method void main(java.lang.String[])

0 getstatic #2 3 ldc #3

5 invokevirtual #4

Saved on the disk

stored on the disk

Source code (developed bythe programmer)

Byte code (generated bythe compiler for JVMto read and interpret, not for you to understand)

Java Bytecode

Java VirtualMachine

AnyComputer

With Java, the sourceprogram is compiled into

a special type of object

code, bytecode.The bytecode can then

run on any computer

with a Java VirtualMachine.

Java Virtual Machine is a

software that interprets

Java bytecode

Method

A collection of statements that performs a

sequence of operations

System.out.println: a method to display a

message on the console

The string argument is enclosed within

parentheses

The main method provides the control of

program flow The Java interpreter executes the application

by invoking the main method

Comments

Three types of comments in Java

Line comment: A line comment is preceded by two

slashes (//) in a line

Paragraph comment: A paragraph comment is

enclosed between /* and */ in one or multiple lines

javadoc comment: javadoc comments begin with /**

and end with */

used for documenting classes, data, and methods

can be extracted into an HTML file using JDK's javadoc

command