1. Object Oriented Programming in java
Dana F. Doghramachi
Chapter -1-
Introduction to OOP
2015

2. What is java ? Designed by Sun Microsystems in 1991. Based on C/C++.
Java used for embedding programs into Web-based applications
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3. Java Features -1- Object Oriented Robust
Object-oriented languages divide programs into separate modules, called objects, that encapsulate the program's data and operations.
Robust
meaning that errors in Java programs don't cause system crashes as often as errors in other programming languages.
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4. Java Features -2- Platform Independent Distributed Language Secure
Platform is a particular kind of computer system, such as a Macintosh or Windows system.
Java program can be run without changes on different kinds of computer system.
Distributed Language
which means that its programs can be designed to run on computer networks.
Secure
Java designed to be used on networks, Java contains features that protect against entrusted code.
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5. Software Development Process -1-
source code is written in TextPad files with the .java extension.
source files are then compiled into .class files by the java compiler.
A .class contains bytecodes: the machine language of the Java Virtual Machine (Java VM).
The java runs the application with an instance of the Java VM
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software development process

6. Software Development Process -2-
Java VM is available on many
different operating systems.
The same .class files are
capable of running on.
Microsoft Windows
Solaris OS
Linux
Mac OS
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7. Writing Java programs We need Creating an Application in Windows
The Java SE Development Kit 8 (JDK 8).
Textpad Or Eclipse.
Textpad.com.
Creating an Application in Windows
Create a source file in .java extension
Compile the source file into a .class java compiler
Run the program
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8. "Hello World!" Application
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9. Comments words in blue color are comments
The Java supports two kinds of comments:
/* text */ or /** documentation */
The compiler ignores everything from /* to */.
// text
The compiler ignores everything from // to the end of the line.
Blank lines, spaces, and tabs are white-space characters Ignored by compiler.
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10. The Class Definition -1-
Begins class declaration for class HelloWorldApp
Every Java program has at least one user-defined class.
Keyword: words reserved for use by Java.
class keyword followed by class name
Naming classes: capitalize every word. //Naming Convention
HelloWorldApp
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11. The Class Definition -2-
Name of class called identifier
Series of characters consisting of letters, digits, underscores ( _ ) and dollar signs ( $ )
Does not begin with a digit, has no spaces //Naming Rules
Examples: Welcome1, $value, _value, button7
7button is invalid
Java is case sensitive (capitalization matters)
a1 and A1 are different
use public keyword // explainlater
Certain details not important now
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12. The Class Definition -3-
Saving files
File name must be class name with .java extension
HelloWorldApp.java
Left brace {
Begins body of every class (line 6)
Right brace ends declarations (line 11)
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13. The main Method Part of every Java application
Applications begin executing at main
Parenthesis indicate main is a method (exp. later).
Java applications contain one or more methods.
Exactly one method must be called main
Methods can perform tasks and return info.
void means main returns no information
Left brace begins body of method declaration
Ended by right brace } (line 10)
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14. Printing a Line of Text Instructs computer to perform an action
Prints string of characters
String - series characters inside double quotes
White-spaces in strings are not ignored by compiler
Method System.out.println
Print to command window (i.e., MS-DOS prompt)
Displays line of text
Argument inside parenthesis
This line known as a statement
Statements must end with semicolon ;
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15. Printing Multi Line of Text
System.out.println( "Welcome\nto\nJava\nProgramming!" );
Notice how a new line is output for each \n escape sequence.
Welcome to
Java
Programming!
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16. Escape characters Backslash ( \ )
Indicates special characters be output
Escape
sequence
Description \ n
Newline. Position the screen cursor at the beginning of the
next line. t
Horizontal tab. Move the screen cursor to the next tab stop. \\
Backslash. Used to print a backslash character.
"
Double quote. Used to print a double -
quote character. For
Example,
System.out.println(
"in quotes
"" );
displays
"in quotes"

17. Displaying Text with printf
The System.out.printf method (f means "formatted") displays formatted data.
System.out.printf("%s%n%s%n", "Welcome to", "Java Programm");
Format specifies begin with a percent sign (%) followed by a character that represents the data type. For example, the format specifies %s is a placeholder for a string.
The format string specifies that printf should output two strings, each followed by a newline character.

18. Java keywords
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19. Primitive Data Types -1-
The eight primitive data types supported by the Java programming language are:
byte:
8-bit signed two's complement integer
minimum value -128
maximum value of 127
short:
16-bit signed two's complement integer
minimum value of -32,768
maximum value of 32,767
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20. Primitive Data Types -2-
int:
32-bit signed two's complement integer
minimum value of -2,147,483,648
maximum value of 2,147,483,647
4. long:
64-bit signed two's complement integer
minimum value of -9,223,372,036,854,775,808
maximum value of 9,223,372,036,854,775,807
byte, short, int, and long are considered as Integral Types
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21. Primitive Data Types -3-
float:
single-precision 32-bit floating point
double:
double-precision 64-bit floating point
boolean:
has only two possible values: true and false
char:
single 16-bit Unicode character
minimum value of '\u0000' (or 0)
maximum value of '\uffff' (or 65,535)
float and double are considered as Floating Point Types
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22. String class
the Java provides special support for character strings via the String class
Enclosing character string within double quotes will automatically create a new String object
for example, String s = "this is a string";
The String class is not a primitive data type
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23. Variables -1-
When the declaration is made, memory space is allocated to store the values of x and y.
x and y are called variables. A variable has three properties:
A memory location to store the value,
The type of data stored in the memory location, and
The name used to refer to the memory location.
Sample variable declarations:
int x; int v, w, y;
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24. Variables -2- float numberOne, numberTwo; long bigInteger;
Here is an example of declaring variables of different data types:
int i, j, k;
float numberOne, numberTwo;
long bigInteger;
double bigNumber;
At the time a variable is declared, it also can be initialized. For example, we may initialize the integer variables count and height to 10 and 34 as in
int count = 10, height = 34;
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25. Variable Types -1-
The Java programming language defines the following kinds of variables:
Instance Variables (Non-Static Fields) objects store their variables in "non-static fields", that is, fields declared without the static keyword.
int cadence = 0;
Class Variables (Static Fields) A class variable is any field declared with the static modifier; this tells the compiler that there is exactly one copy of this variable in existence
static double pi = 3.14;
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26. Variable Types -2-
Local Variables a method will often store its temporary state in local variables
void show(){
int i = 0;
….. }
Parameters the signature for the method is
void changeGear(int newGear){
gear = newGear;
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27. Default Values -1-
Fields that are declared but not initialized will be set to a reasonable default by the compiler.
default will be zero or null, depending on the data type.
Depending on such default values is considered bad programming style.
the compiler never assigns a default value to an uninitialized local variable.
Accessing an uninitialized local variable will result in a compile-time error.
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28. Default Values -2-
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29. Naming Rules and Convention
We mean by naming rules the conditions that should be considered when naming user defined identifiers
User defined identifiers such as variables, methods, classes
If one of these rules is missed when naming an identifier the complier generates an error message
Naming Conventions
Conventions are the rules that is better to be considered when naming an identifier
Missing these convention not cause any errors
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30. Naming Rules (Variables)
Variable names are case-sensitive.
an unlimited-length sequence of Unicode letters and digits.
beginning with a letter, the dollar sign "$", or the underscore character "_“.
White space is not permitted.
Subsequent characters may be letters, digits, dollar signs, or underscore characters.
the name must not be a keyword or reserved word.
Examples for valid variable names:
cadence, x1, _value, $i, bike1 …
Example for invalid variable names:
1y, first Value, one*, void ….
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31. Naming Conventions (Variables)
Use names (not verbs) for variable names.
When choosing a name for your variables, use full words instead of abbreviations.
If the name you choose consists of only one word, spell that word in all lowercase letters.
If it consists of more than one word, capitalize the first letter of each subsequent word, for example gearRatio and currentGear.
If your variable stores a constant value capitalizing every letter and separating subsequent words with the underscore character.
static final int NUM_GEARS = 6;
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32. Naming (Methods and Classes)
Methods Naming
The rules used in naming variables are also applied to method names.
The conventions for methods is the same as for variables except using verbs as methods names.
Classes Naming
The rules used in naming variables are also applied to class names.
The conventions for Classes is the same as for variables except capitalizing the first letter of the class name.
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33. Reading data from keyboard
There are many ways to read data from the keyboard. For example:
InputStreamReader
Console
Scanner
DataInputStream etc.
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34. Scanner Class -1-
Using a Scanner object is a simple way to input data from the standard input System.in, which accepts input from the keyboard.
First we need to associate a Scanner object to System.in as follows:
import java.util.Scanner;
Scanner input= new Scanner(System.in);

35. Scanner Class -2-
public String nextLine(): it moves the scanner position to the next line and returns the value as a string.
public int nextInt(): it scans the next token as an int value.
public double nextDouble(): it scans the next token as a double value.

36. Reading from Standard Input
After the Scanner object is set up, we can read data.
Scanner input= new Scanner(System.in);
System.out.print (“Enter a number: ”);
Int firstNum = input.nextInt();
System.out.println(“The value is :” + firstNum);
1. Prompt is displayed
Enter a number: 25
ENTER
The value is : 25
2. Data is entered
3. Result is printed

37. Application of Adding Integers