The document discusses Java packages and interfaces. It defines that packages are used to organize related classes and avoid naming conflicts. There are built-in and user-defined packages. Interfaces are used to achieve abstraction and multiple inheritance in Java. They contain abstract methods that classes implement. The document provides examples of defining a package with classes, implementing an interface, and using default interface methods.

1. By :
A.Bhuvaneshwari,M.SC(cs)

2.  A package in Java is used to group related
classes. Think of it as a folder in a file
directory. We use packages to avoid name
conflicts, and to write a better maintainable
code. Packages are divided into two
categories:
 Built-in Packages (packages from the Java API)
 User-defined Packages (create your own
packages)

3.  The Java API is a library of prewritten classes,
that are free to use, included in the Java
Development Environment.API is application
program interface.
 Syntax
 Import package.name.Class ;
 // Import a single class
 Import package.name.*;
 // Import the whole package

4.  To create your own package, you need to
understand that Java uses a file system
directory to store them. Just like folders on
your computer:
 Example
 └── root └── mypack └──
MyPackageClass.java

5.  Package packname;
 public class firstClass
 { . . . . . . . . //body of the class.
 . . . . . . .
 }

6.  Java package is used to categorize by the
classes and interfaces.
 It is easy to maintained.
 Java package is provide as access protection.
 It may removes naming collision.
 This packages can be provide reusability of
code.
 We can create our own package or extend
already available pack

7.  To compile the Java programs with package
statements, you have to use -d option as shown
below.
 javac -d Destination_folder file_name.java
 Then a folder with the given package name is
created in the specified destination, and the
compiled class files will be placed in that
folder.

8.  Create package name india and declare the
details:

9.  Package India;
 Public class team
 {
 String name,position,nick;
 Public team(String n,String p,String ni)
 {
 Name=n;
 Position=p;
 Nick=ni;
 }
 Public void display()
 {
 System.out.println(“team India”);
 System.out.println(“name:”+name);
 System.out.println(“position:”+position);
 System.out.println(“nickname:”+nickname);
 }
 }

10.  Import india .team;
 Class pack
 {
 Public static void main(String args[])
 {
 Team c=new team(“dhoni”,”captain”,”cool”);
 C.display();
 }
 }

12.  First create package file and store the package
program.The store main class as the class
name.

13.  Path setting are c:drive,program file,java jdk
version,bin and select the path set as the
command prompt.

14.  Command prompt cd program files,cd java,
 Set path(c:program filejavajdkbin)
 Javac pack.java
 Java pack and get the output

15.  Output:
 Team:india
 Name:dhoni
 position:captain
 Nickname:cool

16.  An interface is a reference type in Java. It is
similar to class. It is a collection of abstract
methods. A class implements an interface,
thereby inheriting the abstract methods of the
interface
 The interface in Java is a mechanism to
achieve abstraction. There can be only abstract
methods in the Java interface, not method
body. It is used to achieve abstraction and
multiple inheritance in Java.

17.  There are mainly three reasons to use interface.
They are given below.
 It is used to achieve abstraction.
 By interface, we can support the functionality
of multiple inheritance.
 It can be used to achieve loose coupling.

18.  interface <interface_name>
 {
 // variable decalaration;
 //methods declaration;
 // by default.
 }
 To declare an interface, use interface keyword. A
class that implements an interface must implement
all the methods declared in the interface. To
implement interface used implements keyword.

19.  Like classes,interface can also be extended.
 That is an interface can be subinterfaced from
other interface.the new subinterface will
inherit all the member of the superinterface in
the manner similar to subclasses.
 SYNTAX
 Interface name2 extends name1
 {
 Body of name2
 }

20.  A class uses the implements keyword to
implement an interface. The implements
keyword appears in the class declaration
following the extends portion of the declaration
 SYNTAX
 Class classname implements interfacename
 {
 Body of classname
 }

21.  Source code:

24.  interface Polygon {
 void getArea();
 default void getSides() {
 System.out.println("I can get sides of polygon.");
 } }
 class Rectangle implements Polygon {
 public void getArea() {
 int length = 6;
 int breadth = 5;
 int area = length * breadth;
 System.out.println("The area of the rectangle is "+area);
 }
 public void getSides() {
 System.out.println("I have 4 sides.");
 } }

25.  class Square implements Polygon {
 public void getArea() {
 int length = 5;
 int area = length * length;
 System.out.println("The area of the square is "+area);
 } }
 class Main { public static void main(String[] args)
 { Rectangle r1 = new Rectangle();
 r1.getArea();
 r1.getSides();
 Square s1 = new Square();
 s1.getArea();
 } }

26.  The area of the rectangle is 30
 I have 4 sides
 The area of the square is 25