FUNDAMENTALS OF JAVA

Compilation Unit• The entire file or .java file is called Compilation Unit

• In Compilation Unit , we can have multiple classes.

• Every Java application has at least one class.

• At least one class has to be public.

Main() method• There is a common signature in every Java program which is an entry point called main() method.

• This is where the Java program starts.

• This is called Starting point for a java class.

Class & Object• Classes are the basis of objects.

• Every java application has at least one class.

• In other words, a class can be defined as a template/blue print that describes the behaviors/states that object of its type support.

• Example of class: blueprint of building a car, a template or model of a building, floor.

Class & Object• A class is can also be considered as a container which holds or stores within it self.

• An object can be defined as an instance of a class.

• Objects have states and behaviors.• States are the properties or attributes in the world of Java.

• Behaviors are the methods or functions in the world of Java.

Class & Object• Example : Object : CarState: color, make, modelBehavior: Drive

• Example : Object :Human BeingsState :name, address -- Properties/AttributesBehavior : Move, dance, work, run, shout -- Methods/Functions

Naming a class• Name of the class is it has to start with _ (underscore), letter, $(dollar) sign .

• Always give some meaningful name which tells you about what your class is saying.

Access Modifiers• public is accessed by any number of classes.

• private is accessible within the class.

• protected is accessible within the class and all the classes within the packages.

More about Java Programming

• Java is --Case Sensitive

--Does not really care about white space. That means does not really requires indentation.

--Statements always ends with semi-colon(;)

Comments• Comments are notes or documents or keypoints about your program.

• Compiler ignores everything that is writen in between the slashes.

• Categorized as two types:• Single line commentsEg: // displaying the output

• Multiple line comments Eg: /******************* These are my comments *********** */

Keywords• Keywords are always constant and we can never change them.

• public • static • void • System• For• If• …………etc

Java Data Types

• Java Data Types are of two types:

• Primitive Data Types : System build datatypes which cannot be broken down.

• User Defined Types : Users define the data types.

Java Data Types• Primitive Data Types are of 8 types:

• byte -- 8bits • short -- 16bits• int – 32 bits• long – 64bits• float– 32 bits• double – 64 bits• char– 8bits• boolean - 8 bits

Examples

long ssn = 999999999L; float pi = 3.1415F; int var = 123;

char letter =‘a’; boolean one =true; double =1244.5;

Examples