1. Sampath Kumar S Assistant Professor, SECE
Packages
Sampath Kumar S
Assistant Professor, SECE

2. 12/31/2018
Packages
A package is a group of similar types of classes, interfaces and sub-packages.
(Or)
A Package can be defined as a grouping of related types(classes, interfaces, enumerations and annotations ) providing access protection and name space management.
Package can be categorized in two form,
built-in package (java, lang, awt, javax, swing, net, io, util, sql etc)
user-defined package.
The package keyword is used to create a package.
Sampath Kumar S, AP

3. 12/31/2018
Advantage of Package?
Package is used to categorize the classes and interfaces so that they can be easily maintained.
Package provides access protection.
Package removes naming collision.
Sampath Kumar S, AP

4. 12/31/2018
Example of package
//save as Simple.java package mypack; public class Simple{ public static void main(String args[]){ System.out.println("Welcome to package"); } }
Sampath Kumar S, AP

5. 12/31/2018
Compiling the Package
If you are not using any IDE, you need to follow the syntax given below:
javac -d directory <javafilename>
Example:  
javac -d . Simple.java 
Note: 
The -d switch specifies the destination where to put the generated class file.
You can use any directory name like /home (in case of Linux), d:/abc (in case of windows) etc.
If you want to keep the package within the same directory, you can use . (dot).
Sampath Kumar S, AP

6. Run the Package To Compile: javac -d . Simple.java
12/31/2018
Run the Package
To Compile: javac -d . Simple.java
To Run: java mypack.Simple
Note:
The -d is a switch that tells the compiler where to put the class file i.e. it represents destination.
The .(dot) represents the current folder.
We need to use fully qualified name
e.g: mypack.Simple to run the class
Sampath Kumar S, AP

7. Accessing package from another package
12/31/2018
Accessing package from another package
There are three ways to access the package from outside the package.
import package.*;
import package.classname;
fully qualified name.
Sampath Kumar S, AP/IT

8. 1. Using packagename.*
12/31/2018
If we use “package.*” then all the classes and interfaces of this package will be accessible but not subpackages.
The import keyword is used to make the classes and interface of another package accessible to the current package.
Sampath Kumar S, AP

9. Example: packagename.*
12/31/2018
Example: packagename.*
//save by A.java  
package pack;  
public class A {  
  public void msg(){
System.out.println("Hello");
}  
Sampath Kumar S, AP

10. Example: Cont.., Output: Hello //save by B.java package mypack;
12/31/2018
Example: Cont..,
//save by B.java  
package mypack;  
import pack.*;     
class B{  
  public static void main(String args[]){  
   A obj = new A();  
   obj.msg();  
  }  
}  
Output: Hello
Sampath Kumar S, AP

11. 2. Using Packagename.classname
12/31/2018
If we import “package.classname” then only declared class of this package will be accessible.
Sampath Kumar S, AP

12. Example: Packagename.classname
12/31/2018
Example: Packagename.classname
//save by A.java  
package pack;  
public class A {  
  public void msg(){
System.out.println("Hello");
}  
Sampath Kumar S, AP

13. Example: Cont.., Output: Hello //save by B.java package mypack;
12/31/2018
Example: Cont..,
//save by B.java  
package mypack;  
import pack.A;     
class B{  
  public static void main(String args[]){  
   A obj = new A();  
   obj.msg();  
  }  
}  
Output: Hello
Sampath Kumar S, AP

14. 3. Using fully qualified name
12/31/2018
3. Using fully qualified name
If we use fully qualified name then only declared class of this package will be accessible.
Now there is no need to import.
But we need to use fully qualified name every time when we are accessing the class or interface.
It is generally used when two packages have same class name e.g. java.util and java.sql packages contain Date class.
Sampath Kumar S, AP

15. Example: Packagename.classname
12/31/2018
Example: Packagename.classname
//save by A.java  
package pack;  
public class A {  
  public void msg(){
System.out.println("Hello");
}  
Sampath Kumar S, AP

16. Example: Cont.., Output: Hello //using fully qualified name
12/31/2018
Example: Cont..,
//save by B.java  
package mypack;  
import pack.A;     
class B{  
  public static void main(String args[]){  
    pack.A obj = new pack.A();
//using fully qualified name    
    obj.msg();  
  }  
}  
Output: Hello
Sampath Kumar S, AP

17. Note: If we import a package, subpackages will not be imported.
12/31/2018
Note:
If we import a package, subpackages will not be imported.
If we import a package, all the classes and interface of that package will be imported excluding the classes and interfaces of the subpackages. Hence, we need to import the subpackage as well.
Sampath Kumar S, AP

18. 12/31/2018
Subpackage
Package inside the package is called the subpackage. It should be created to categorize the package further.
The standard of defining package is domain.company.package
e.g. in.sece.it
Sampath Kumar S, AP

19. Example: Output: IT a Subpackage of SECE
12/31/2018
Example:
package in.sece.it; class Simple{ public static void main(String args[]){ System.out.println(“IT a Subpackage of SECE"); } } Note: To Compile: javac -d . Simple.java To Run: java in.sece.it.Simple
Output: IT a Subpackage of SECE
Sampath Kumar S, AP

20. Ways to load the class files or jar files
12/31/2018
Ways to load the class files or jar files
There are two ways to load the class files temporary and permanent.
Temporary
By setting the classpath in the command prompt
By -classpath switch
Permanent
By setting the classpath in the environment variables
By creating the jar file, that contains all the class files, and copying the jar file in the jre/lib/ext folder.
Sampath Kumar S, AP

21. Send the class file to another directory or drive
12/31/2018
Send the class file to another directory or drive
If want to put the class file of A.java source file in classes folder of c: drive
Sampath Kumar S, AP

22. 12/31/2018
Example:
//save as Simple.java package mypack; public class Simple{ public static void main(String args[]){ System.out.println("Welcome to package"); } }
Sampath Kumar S, AP

23. 12/31/2018
Cont..,
To Compile: e:\sources> javac -d c:\classes Simple.java To Run: (Method 1) To run this program from e:\source directory, we need to set classpath of the directory where the class file resides. e:\sources> set classpath=c:\classes;.; e:\sources> java mypack.Simple
Sampath Kumar S, AP

24. 12/31/2018
Cont..,
To Run: (Method 2)
Another way to run this program by “-classpath” switch of java.
The “-classpath” switch can be used with javac and java tool. To run this program from “e:\source“ directory, we can use “-classpath” switch of java that tells where to look for class file.
For example:
e:\sources> java -classpath c:\classes mypack.Simple
Sampath Kumar S, AP

25. Ways to load the class files or jar files
12/31/2018
Ways to load the class files or jar files
There are two ways to load the class files temporary and permanent.
Temporary
By setting the classpath in the command prompt
By -classpath switch
Permanent
By setting the classpath in the environment variables
By creating the jar file, that contains all the class files, and copying the jar file in the jre/lib/ext folder.
Sampath Kumar S, AP

26. 12/31/2018
Sampath Kumar S, AP

27. 12/31/2018
Thank You 
Sampath Kumar S, AP