Chapter 3 Pacakge

1. Packages
JADHAV S. B.
Chap- 3

2. Chapter 3
Packages & Interfaces
S.NO. TOPIC
1 Defining, Creating and Accessing a Package
2 Importing packages
3 Differences between classes and interfaces
4 Defining an interface
5 Implementing interface
6 Applying interfaces
7 variables in interface and extending interfaces
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3. Java Packages:
 Its special library where the group of similar
types of classes are stored.
 Packages are act as “containers” for classes.
 Packages are stored in hierarchical manner.
 Java packages are divided into two types
1. Java API Packages
2. User Defined Packages
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4. Java API Packages:
 Java API provides a number of classes groped
into different packages according to their
functionality.
 Java API Packages are:
- lang (import java.lang.*)
- util (import java.util.*)
- io (import java.io.*)
- awt (import java.awt.*)
- net (import java.net.*)
- applet (import java.applet.*)
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5. java.lang.*;
 This package contains language support
classes.
 It includes classes for
- primitive types, strings, math functions,
threads & exceptions.
Syntax to import lang package:
import java.lang.*;
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6. Java.util.*;
 This is the language utility classes such as
- vectors, hash tables, random numbers, data
etc..
 Syntax to import util package:
import java.util.*;
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7. Java.io.*;
 This package contains input/output support
classes.
 They provide facilities for input/output of data.
- DataInputStream, DataoutputStream,
Bufferedreader etc…
 Syntax to import io package:
import java.io.*;
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8. Java.awt.*;
 This package contains the set of classes
implementing graphical user interface(GUI).
 They include classes for
- windows, buttons, lists, menus and so on..
 Syntax to import awt package:
import java.awt.*;
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9. Java.net.*;
 It contains the classes for networking.
 They include classes for communication with
local computers as well as with internal servers.
 Syntax to import net package:
import java.net.*;
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10. Java.applet.*;
 It contains the classes for creating and
implementing applets.
 Syntax to import applet package:
import java.applet.*;
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11. User Defined Package
 As predefined packages we can create our own
packages called user defined packages.
 To create user defined package following steps
are required.
1. Declare a package
2. Define a class
3. create sub directory under main directory.
4. Store the packages into subdirectory.
5. Compile the source file.
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12. User Defined Package
1. Declare a package at the beginning of the file
using the form.
 Package package_name;
‘package’ is the keyword followed by package
name.
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13. User Defined Package
2. Define a class which is to be put in the package
& declare it as public.
 Syntax:
package firstpackage;
public class firstclass
{
-----------
-----------
}
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14. User Defined Package
3. Create a subdirectory under the directory where
the main source file is stored.
4. Store the listing of files, in the subdirectory
created.
5. Compile the source file in the subdirectory.
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15. Accessing a Package
 The java system packages are accessed by
using
1. Fully qualified class name
OR
2.Through a import statement
1 import firstpackage.firstclass;
2  import packagename.*;
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16. Creating a Package
 A package statement inserted as the first line of
the source file:
package Package1;
public class classX
{
public void displayx()
{
System.out.println(“ClassX”)
}
}
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17. Creating a Package
package Package2;
public class ClassY
{
public void displayy()
{
System.out.println("ClassY");
}
}
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18. Creating a Package
import Package1.ClassX;
import Package2.*;
public class PackageTest
{
public static void main(String a[])
{
ClassX x=new ClassX();
ClassY y=new ClassY();
x.displayx();
y.displayy();
}
}
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19. Output:
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20. Package Example:
package Pack_A;
import java.io.*;
import java.lang.*;
public class ClassA
{
int rollno;
String name;
BufferedReader br=new BufferedReader(new
InputStreamReader(System.in));
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21. Package Example:
public void getinfo()
{
try {
System.out.println("Enter roll no & name of student:");
rollno=Integer.parseInt(br.readLine());
name=br.readLine();
}
catch(Exception e)
{
System.out.println(e);
}
}
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22. Package Example:
public void putinfo()
{
System.out.println("RollNo="+rollno);
System.out.println("Name="+name);
}
}
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23. ClassB:
package Pack_B;
import java.io.*;
import java.lang.*;
public class ClassB
{
int m1,m2,m3;
double avg;
BufferedReader br=new BufferedReader(new
InputStreamReader(System.in));
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24. ClassB:
public void getdata()
{
try
{
System.out.println("Enter the marks of 3 subject:");
m1=Integer.parseInt(br.readLine());
m2=Integer.parseInt(br.readLine());
m3=Integer.parseInt(br.readLine());
avg=(m1+m2+m3)/3;
}
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25. ClassB:
catch(Exception e) {
System.out.println(e);
}
}
public void putdata()
{
System.out.println("Marks1="+m1);
System.out.println("Marks2="+m2);
System.out.println("Marks3="+m3);
System.out.println("Average="+avg);
}
}
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26. PackageDemo.java
import Pack_A.ClassA;
import Pack_B.*;
public class PackageDemo{
public static void main(String args[]) {
ClassA a=new ClassA();
ClassB b=new ClassB();
a.getinfo();
a.putinfo();
b.getdata();
b.putdata();
}
}
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27. Output:
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28. Importing of Packages
 Since classes within packages must be fully-
qualified with their package names, it would
be tedious to always type long dot-separated
names.
 The import statement allows to use classes
or whole packages directly.
 Importing of a concrete class:
import myPackage1.myPackage2.myClass;
 Importing of all classes within a package:
import myPackage1.myPackage2.*;
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29. Import Statement
 The import statement occurs immediately after the
package statement and before the class statement:
package myPackage;
 import otherPackage1;otherPackage2.otherClass;
class myClass { … }
 The Java system accepts this import statement by
default:
import java.lang.*;
 This package includes the basic language functions.
Without such functions, Java is of no much use.
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