lec 4 06_aug [compatibility mode]
TRANSCRIPT
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ObjectObject--Oriented ProgrammingOriented Programming
Lecture 4
Naveen Kumar
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ObjectObject
An object is anything that can be represented by data in a computer’s memory and manipulated by a computer program.
Numbers, texts, pictures, sound, video ….. So on
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ObjectObject
An object can be something in the physical world or even just an abstract idea.
for example: An airplane, is a physical
object that can be manipulated by a
computer.
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ObjectObject
A bank transaction is an example of an object that is not physical.
To a computer,
an object is simply something that can be represented by data in the computer’s memory and manipulated by computer programs
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ObjectObject
The data that represent the object are organized into a set of properties.
NameName: : AI 379AI 379
OwnerOwner:: Indian AirlinesIndian Airlines
LocationLocation:: 39 52′ 06″N39 52′ 06″N 75 13′ 52″W 75 13′ 52″W
HeadingHeading:: 271271°°
AltitudeAltitude:: 19 m19 m
AirSpeedAirSpeed:: 00
MakeMake:: BoeingBoeing
ModelModel:: 737737
WeightWeight:: 32,820 kg32,820 kg
The values stored in an object’s properties, at any one time, form the stateof an object.
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ObjectObject--Oriented ProgrammingOriented Programming
Computer programs implement algorithms that manipulate the data.
In object-oriented programming, the programs that manipulate the properties of an object are the object’s methods.
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ObjectObject--Oriented ProgrammingOriented Programming
We can think of an object as a collection of propertiesand, the methods that are used to manipulate those properties.
Properties
Methods
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ObjectObject--Oriented ProgrammingOriented Programming
A class is a group of objects with the same properties and the same methods.
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ObjectObject--Oriented ProgrammingOriented Programming
Each copy of an object, from a particular class is called an instance, of the object.
The act of creating a new instance of an object is called instantiation.
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ObjectObject--Oriented ProgrammingOriented Programming
A class can be thought of as a blueprint for instances of its object.
Two different instances of the same class will have the same properties, but different values stored in those properties.
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ObjectObject--Oriented ProgrammingOriented Programming
The same terminology is used in most object-oriented programming languages.
Object
Instance
Property
MethodInstantiation
ClassState
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Introduction to Java
12
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Development tools-part of java development kit (JDK) Classes and methods-part of Java Standard Library (JSL),
also known as Application Programming Interface (API)
1. JDK: Appletviewer ( for viewing applets) Javac (Compiler) Java (Interpreter) Javah (for C header files) Javadoc ( for creating HTML description)
Java Environment
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2. Application Package Interface (API)Contains hundreds of classes and methods grouped into several functional packages: Language Support Package (String, Integer, Double, etc) Utility Packages (rand. num. gen., sys. date) Input/Output Packages Networking Packages (implementing networking appl. ) AWT Package (classes for painting graphics and images) Applet Package (web page using java)
Java Environment
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1. Java 1.0 (96)2. Java 1.1 (97)(Add new library, redefine applet handling and
reconfigured many features.)3. Java 2 (98)(Second generation). Version no:1.2 (Internal
version number of java library). Also known as J2SE [ Java 2 Platform Standard Edition].- Add swing, the collection framework, enhanced JVM etc.
4. J2SE 1.3 (2000)5. J2SE 1.4 (2002)6. J2SE 1.5 (2004)7. J2SE 1.6 (2006) [1.7-(2013), in queue 1.8 (exp in 2014) ]
The Evolution of Java
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Comments
In Java, comments are preceded by two slashes (//) in a line, orenclosed between /* and */ in one or multiple lines
When the compiler sees //, it ignores all text after // in the same line
When it sees /*, it scans for the next */ and ignores any text between /* and */
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Example
/* Traditional "Hello World!" program. */
// package pack1; // import java.lang.System; class A { public static void main (String args[]) { System.out.println("Hello World!");
} }
Save program as A.java
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Java Program Structure
Package Statement Javac command compiles the source code A.java then,
generates A.class and store it under a directory which is called as name of the package
package statement if used must be the first statement in a compilation unit. Its syntax is:
package packageName; For example:
package pack1;
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Import Statement
The import statements are similar to #include statements in C and C++
In the above program, System class of java.lang package is imported into all Java programs by default. The syntax of import statement is as:
import fullClassName;
For example, the following import statement imports the System class from java.lang:
import java.lang.System;import java.lang.*;
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Classes and Methods
Class declarations contain a keyword class and an identifier (Ex: A) Class members are enclosed within braces. The syntax of defining a
class is shown below:
class A{ // program code
}
To execute a class, it must contain a valid main method It is the first method that automatically gets invoked when the program
executed
public static void main (String args[]){
//instructions }