Session 7:- Package In java.

Introduction about packages:-

•  Package is nothing but it is folder.
•  In java we use packages for better Maintains of the application, project search easily.
• Every package can have direct classes or it can have again package (sub packages).
• To access any member (instance variable, instance method etc) outside the package but the member should be public.
• Within package we no need to import class of the package. 
•  * will import all the class which is directly under the package (not a sub package).  
• We can’t import more than same java file having the different package. 
• All 3000+ inbuilt java class. Modularizes many packages.
• Ex. - java.lang.*;
•  -java.sql.*;
•   - java.io.*;
• - java.util.*;
• - java.awt.*;

• All the class which is under java.lang package will be available implicitly and we don’t have to import. 
•  Package declaration must be first executable statement.  
• De-referred object which are present in heap will be collected by Garbage Collector and re-uses memory. 
• When object in which is present in heap can have multiple reference. 
• But single reference can refer or point to only one object at same time or given time.  
• When an instance is of primitive Data type that is called as HAS-A Relationship.   
• When an instance of variable is non-primitive data type that is called as Association Relationship. 

Example 9:- Package

public class Person{

            // instance variable

        int age=25; //HAS-Relationship

String name="JNext Training & Development !!!!!! SUPER"; // Association Relationship

Mobile m; //Association Relationship

// some Method

 }

public class Mobile

{

    double price; //HAS-Relationship

    String company_name; // Association Relationship

    // some method }