1 Intro+Var Data Types

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Object-OrientedProgramming (2)

OOP2

Introduction

Variables, Constants and Built-in Data TypesJava Program Structure


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Outline

What a computer is

What a computer program is

The Programmers Algorithm How a program that you write in Java is

changed into a form that your computer canunderstand

Characteristics of Java Variables, Constants and Built-in Data Types

Java Program Structure


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What Is a Computer?

Computer

Executes statements (computations/logical decisions)

Hardware :Physical devices of computer system

Software: Programs that run on computers

Control Unit

Arithmetic/Logic Unit

Memory Unit

Input device Output Device

Central Processing Unit

My ProgamMy data


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Computer Organization

Six logical units of computer system

Input unit (Mouse, keyboard)

Output unit (Printer, monitor, audio speakers) Memory unit (Retains input and processed information)

Central processing unit (CPU) which consists of:

Control unit (Supervises operation of other devices)

Arithmetic and logic unit (ALU) (Performs calculations)

Secondary storage unit (Hard drives, floppy drives)


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What a computer program is?

For a computer to be able to perform specifictasks (i.e. print what grade a student got onan exam), it must be given instructions to do

the task.

The set of instructions that tells the computerto perform specific tasks is known as acomputer program


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Levels of ProgramDevelopment

Human thought

Pseudo-Natural Language (English, Arabic)

High Level Programming Language (C, C++,Java, )

Machine Code


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The Programmers Algorithm

An algorithm is a finite sequence ofinstructions that produces a solution toa problem.

The programmers algorithm: Define the problem

Plan the problem solution

Code the program.

Compile the program.

Run the program.

Test and debug the program.


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Defining the Problem The problem must be defined in terms of:

Input: Data to be processed.

Output: The expected result.

Look for nouns in the problem statement that suggest output andinput.

and processing: The statements to achieve. Look for verbs to suggest processing steps.

Keyboard ScreenProcessing

input data output data


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Input and Output

Inputs Can come from many sources, such as users,

files, and other programs

Can take on many forms, such as text, graphics,

and sound

Outputs Can also take on many forms, such as numbers,

text, graphics, sounds, or commands to otherprograms


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Example:Area and Perimeter of a circle

Input

Radius

PI

ProcessingArea = PI * Radius * Radius

Perimeter = 2 * PI * Radius

Output

Area Perimeter


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Planning the Solution

When planning, algorithms are used tooutline the solution steps usingEnglishlike statements, called

pseudocode.


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Coding the Program

Coding is writing the program in a formal languagecalled Programming Language.

Programming Language : A set of rules, symbols and specialwords used to write statements.

The program is written by translating the algorithmsteps into a programming language statements.

The written program is called Source codeand it issaved in a file with .java extension.

Program

Coding

Algorithm Pseudocode

Source Code(The .java)

Translating


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Compiling Computer Programs

Computers do not understandprogramswritten in programming languagessuch asC++ and Java

Programsmust first be convertedintomachine codethat the computer can run

A Software that translatesa programminglanguage statements into machine code iscalled a compiler

Machine code

Program Source code

Machine Code

TranslatingCompiling


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Programming Language Compiler

A compiler is a software that: Checks the correctnessof the source code

according to the language rules.

Syntax errors are raised if some rules wereviolated.

Translatesthe source code into a machinecode if no errors were found.


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Platform dependent Compiling

Because different platforms, or hardwarearchitectures along with the operating systems(Windows, Macs, Unix), require different

machine code, you must compi le mostprograms separately for each platform.


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Compiling Java Programs

The Java compiler produces bytecode(a .classfile)not machine code from the source code (the

.java file).

Bytecode is converted into machine code using aJava Interpreter

Source Code Bytecode


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Platform IndependentJava Programs Compiling

You can run bytecode on an computer thathas a Java Interpreter installed

Hello.java Hello.class


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Multipurpose Java Compiling


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Running The Program

ClassLoader

BytecodeInterpreter

BytecodeVerifier

Hardware

Operating System

JVMThe Bytecode(the .class file)

Running


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The Java Virtual MachineComponents

The Class Loader stores bytecodes in memory

Bytecode Verifier ensures bytecodes do not violate securityrequirements

Bytecode Interpreter translates bytecodes into machine language


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The Java Virtual Machine

The class Loader, the BytecodeVerifierand Interpreter constitute the Java VirtualMachine (JVM).

JVM is platform specific.

The interpreter translates the bytecodes

into specific machine commands.

T ti d D b i th


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Testing and Debugging theProgram

Testing Be sure that the output of the program

conforms with the input.

There are two types of errors:

Logical Errors:The program run but provideswrong output.

Runtime errors:The program stop runningsuddenly when asking the OS executing a noneaccepted statement (divide by zero, etc).

Debugging

Find, Understand and correct the error


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Primary

Memory

.

.

.

.

.

.

Disk

Disk

Disk

Editor

Compiler

Class Loader

Program is created inan editor and stored ondisk in a file ending with.java.

Compiler createsbytecodes and storesthem on disk in a fileending with .class.

Class loader reads.class filescontainingbytecodes from diskand puts thosebytecodes inmemory.

Phase 1

Phase 2

Phase 3

PrimaryMemory

.

.

.

.

.

.

Bytecode Verifier Bytecode verifierconfirms that allbytecodes are validand do not violateJavas securityrestrictions.

Phase 4

PrimaryMemory

.

.

.

.

.

.

InterpreterInterpreter readsbytecodes andtranslates them into alanguage that thecomputer canunderstand, possiblystoring data values asthe programexecutes.

Phase 5

JavaDevelopmentEnvironment


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Some Characteristics of Java

Object-Oriented Combines data and behavior into one unitobjects

Provides Data abstraction and encapsulation

Decomposeprogramintoobjects.

Programs are collections of interacting and cooperating objects. Platform-independent

Portable

Architecture neutral

Write-once, run-anywhere

Secure The bytecode verifier of the JVM :

checks untrusted bytecode

controls the permissions for high level actions.


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Variables, Constants and Built-in Data TypesJava Program Structure

Discovering what is a variable

Discovering what is a data type

Learning about the basic data types

Constants and variables identifiers

Get acquainted with how to select propertypes for numerical data.

Write arithmetic expressions in Java.

Program Structure.


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Programs and Data

Most programs require the temporary storage of data.The data to be processed is stored in a temporary storagein the computer's memory: space memory.

A space memory has three characteristics Identifier

Data Type

State

Keyboard ScreenProcessing

input data output data


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State of the Space Memory

The state of the space memoryis thecurrent value (data) stored in the spacememory.

The state of the space memory: May be changed.

In this case the space memory is called variable.

Cannot be changed.

In this case the space memory is called constant.


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Space Memory Identifier Identifier is a sequence of characters that

denotes the name of the space memory tobe used.

This name is unique within a program.

Identifier Rules

It cannot begin with a digit (0 9).

It may contain the letters a to z, A to Z, thedigits 0 to 9, and the underscore symbol, _.

No spaces or punctuation, except theunderscore symbol, _, are allowed.


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Constants:

All uppercase, separating words withina multiword identifier with theunderscore symbol, _.

Variables

All lowercase.

Capitalizing the first letter of each wordin a multiword identifier, except for thefirst word.

Identifier Conventions in Java


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Identifiers are Case-Sensitive

Identifiers in Java are case-sensitive. Thus,the identifiers myNumber and mynumber,are seen as two different identifiers by thecompiler.


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Data Type

The data type defines what kinds of values aspace memory is allowed to store.

All values stored in the same space memoryshould be of the same data type.

All constants and variables used in a Javaprogram must be defined prior to their use in

the program.


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Java built-in Data Types

Constant or Variable

Numeric Character Boolean

Integer Floating-point

short

int

char String boolean

float

double

First Decision Level

Second Decision Level

Third Decision Level

Fourth Decision Level

long

byte

P i iti D t T


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Primitive Data TypesType

Size(bits)

Range Description

boolean true, false Stores a value that is eithertrue or false.

char 16 0 to 65535 Stores a single 16-bitUnicode character.

byte 8 -128 to +127 Stores an integer.

short 16 -32768 to +32767 Stores an integer.

int 32 bits -2,147,483,648 to+2,147,483,647

Stores an integer.

long 64 bits -9,223,372,036,854,775,808to+9,223,372,036,854,775,807

Stores an integer.

float 32 bits accurate to 8 significant digits Stores a single-precisionfloating point number.

double 64 bits accurate to 16 significant digits Stores a double-precisionfloating point number.


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Variable/Constant Declaration

When the declaration is made, memory spaceis allocated to store the values of the declaredvariable or constant.

The declaration of a variable means allocatinga space memory which state (value) maychange.

The declaration of a constant means allocatinga space memory which state (value) cannotchange.


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Constant Declaration

final dataType constIdentifier = literal | expression;

final double PI = 3.14159;final int MONTH_IN_YEAR = 12;final short FARADAY_CONSTANT = 23060;

final int MAX = 1024;

final int MIN = 128;final int AVG = (MAX + MIN) / 2;

These are constants,also called namedconstant.

The reserved wordfinal is used todeclare constants.

These are calledliterals.

This is calledexpression.


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Variable Declaration

A variable may be declared: With initial value.

Without initial value.

Variable declaration with initial value;dataType variableIdentifier = literal | expression;

double avg = 0.0;int i = 1;

int x =5, y = 7, z = (x+y)*3;

Variable declaration without initial value;dataType variableIdentifier;

double avg;int i;



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// import Section import used java libraries

public classMyProgramName {

// main method

public static voidmain( String args[] ){

// Declaration section Declare needed variables

// Input section Enter required data

// Processing section Processing Statements

// Output section Display expected results

}// end main

}// end class


Salam Program


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// import section: Empty

public classMySalamProgram{

// main method

public static voidmain( String args[] ){

// Declaration section: Empty

// Input section: Empty

// Processing section: Empty

// Output sectionSystem.out.println( SalamaHello);

}// end main

}// end class

Salam Program

S i C ili d R i


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Saving, Compiling and RunningJava Programs

Saving a Java program.A file having a name same as the class name should

be used to save the program. The extension of thisfile is .java.

Salam program should be saved in a file called

MySalamProgram.java. Compiling a Java program.

Call the Java compilerjavac: javacMySalamProgram.java

The Java compiler generates a file called MySalamProgram.class(the bytecode).

Running a Java program Call the Java Virtual Machinejava:

javaMySalamProgram.class

Comments in a Java Program


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Comments in a Java Program

Commentsare used to describe what your code doesand aid reading your code.

The Java compiler ignores them. Comments are made using

//, which comments to the end of the line, or/* */, everything inside of it is considered a comment

(including multiple lines). The comment begins after the first/*.It ends just before the first */.

Examples:

/*This comment begins at this line.This line is included in this commentIt ends at this line. */

//This comment starts here and ends at the end of this line.

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1 Intro+Var Data Types