This document discusses Java programming packages. It explains that Java API provides predefined packages organized by functionality. Packages are hierarchical, so classes can be accessed using package names and dot notation. The import statement allows accessing package classes without fully qualifying names. To create a package, the package keyword declares the name, then classes within that package are defined and stored in a subdirectory matching the package name. Packages can be accessed using import or fully qualifying class names with the package path.

1. Programming in JAVA
by
S. Thanga rathinam(181619)
M.Vivek mani(181620)
II B.Sc Mathematics(CA)
SBK College,Aruppukottai
TO
K.Padma Priya M.Sc(CS),M.Phill.
Assistant professor
Dept of mathematics(CA)
SBK College,Aruppukottai

2. Packages
Java API packages
Using system packages
Naming conventions
Creating packages
Accessing package

3. JAVA API packages:
JAVA API provides a large number of classes
grounded into a different packages according to
functionality. Most of the time we use the packages
available with the java API.
JAVA
lang util io awt net applet

4. Using system packages:
The packages are organaised in hierarchical
structure . The packages named java contains the
package awt which turn contains various classes
required for implementing graphical user interface.
There are two ways of accessing the class stored
in a packages.this is done by using the packges name
containing the class and then appending the class
name to it using the dot operator.

5. java.awt.colour
We want to use the class in a number of places in the
program or we may like to use many of the classes
contained in a package.
import packagename .*;
or
import packagename.classname;
These are known as import statements and must appear at
the top of the file,before any class declarations,import is a
keyword.

6. Naming conventions:
Packages can be named using the standard
java naming rules. By convention, however ,packages
begin with lowercase letters.
double y = java.lang.math.sqrt(x);
package class method
name name name
This statement uses a fully qualifed class name
math to invoke the method sqrt().

7. Creating packages:
we must first declare the name of the packages
using the package keyword followed by a package
name.
package first package;
public class firstclass
{
………….
……….... (body of class)
………….
}

8. Declare the package at the beginning of a file using the
form
package packagename;
Define the class that is to be put in the package
anddeclare it public .
Create a subdirectory under the directory where the main
source files are stored.
Store the listing as the classname .java file in the
subdirectory created.
Compile the file. This creates .class file in the
subdirectory.

9. Accessing a package:
The same approaches can be used to access the
user defined packages as well. The import statement can
be used to search the list of packages for a particular
class.
Import package 1[.package2] [.package3].
classname;
The import statement should appears before any class
definitions in a source file. Multiple import statements
are allowed.

10. Import first package.second package.myclass;
The statement must end with a semicolon(;).

11. Thankyou