A Package MCA which has one class Student. Accept student detail through
parameterized constructor. Write display () method to display details. Create a
main class which will use package and calculate total marks and percentage.
Packages in Java is a mechanism to encapsulate a group of classes,
interfaces and sub packages. Many implementations of Java use a hierarchical
file system to manage source and class files. It is easy to organize class
files into packages. All we need to do is put related class files in the same
directory, give the directory a name that relates to the purpose of the
classes, and add a line to the top of each class file that declares the package
name, which is the same as the directory name where they reside.
In java there are already many predefined packages that
we use while programming.
For example: java.lang, java.io, java.util etc.
However one of the most useful feature of java is that we can define our own packages
However one of the most useful feature of java is that we can define our own packages
Advantages
of using a package
·
Reusability: Reusability of code is one of the most
important requirements in the software industry. Reusability saves time, effort
and also ensures consistency. A class once developed can be reused by any
number of programs wishing to incorporate the class in that particular program.
·
Easy to locate the files.
·
In real life situation there may arise scenarios where we need
to define files of the same name. This may lead to “name-space collisions”.
Packages are a way of avoiding “name-space collisions”.
Types of package:
1.
Built-in package:
The already defined package like java.io.*, java.lang.* etc are known as
built-in packages.
2.
User defined package: The package we create is
called user-defined package.
Built-in Packages
These packages consist of a large number of classes which are a part of Java API.Some of the commonly used built-in packages are:
1) java.lang: Contains language support classes(e.g classed which defines primitive data types, math operations). This package is automatically imported.
2) java.io: Contains classed for supporting input / output operations.
3) java.util: Contains utility classes which implement data structures like Linked List, Dictionary and support ; for Date / Time operations.
4) java.applet: Contains classes for creating Applets.
5) java.awt: Contain classes for implementing the components for graphical user interfaces (like button , ;menus etc).
6) java.net: Contain classes for supporting networking operations.
These packages consist of a large number of classes which are a part of Java API.Some of the commonly used built-in packages are:
1) java.lang: Contains language support classes(e.g classed which defines primitive data types, math operations). This package is automatically imported.
2) java.io: Contains classed for supporting input / output operations.
3) java.util: Contains utility classes which implement data structures like Linked List, Dictionary and support ; for Date / Time operations.
4) java.applet: Contains classes for creating Applets.
5) java.awt: Contain classes for implementing the components for graphical user interfaces (like button , ;menus etc).
6) java.net: Contain classes for supporting networking operations.
User defined
package
Creating
a Package
While creating a package, you should choose a name for the package
and include a package statement along with that name at the
top of every source file that contains the classes, interfaces, enumerations,
and annotation types that you want to include in the package.
The package statement should be the first line in the
source file. There can be only one package statement in each source file, and
it applies to all types in the file.
If a package statement is not used then the class,
interfaces, enumerations, and annotation types will be placed in the current
default package.
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.
Defining a Package:
This statement should be used in the beginning of the
program to include that program in that particular package.
package <package name>;
package <package name>;
Use package keyword
Is very first statement in JAVA program
package
pkg_name;
if you want to create sub-packages
package rootPackage.subPackage1;
Must have exactly one public class
If you want more than one public class in same package
then create different files for each public class.
Save JAVA program with public class class_name
. public
class class_name {
}
Example
Let us look at an example that creates a package
called animals. It is a good practice to use names of packages with
lower case letters to avoid any conflicts with the names of classes and
interfaces.
Following package example contains interface named animals −
package
animals;
interface Animal {
public void eat();
public void
travel();
}
Now, let us implement the above interface
in the same package animals
package
animals;
/* File name :
MammalInt.java */
public class MammalInt implements Animal {
public void eat() {
System.out.println("Mammal
eats");
}
public void
travel() {
System.out.println("Mammal
travels");
}
public int
noOfLegs() {
return 0;
}
public static void
main(String args[]) {
MammalInt m = new MammalInt();
m.eat();
m.travel();
}
}
Now compile the java files as shown below
−
$ javac -d . Animal.java
$ javac -d . MammalInt.java
Now a package/folder with the name animals will
be created in the current directory and these class files will be placed in it.
You can execute the class file within the
package and get the result as shown below.
Mammal eats
Mammal travels
The
import Keyword
If a class wants to use another class in the same package,
the package name need not be used. Classes in the same package find each other
without any special syntax
Algorithm:-
- Start
- create
package MCA.
- Define class Student
with its attributes, parameterized
constructor and methods in package MCA.
- Create a main
program with class name package_Demo
- Import MCA
to main program
- Create object
of Student class inside main class.
- Invoke
display() method of Student class on that object to display total marks
and percentage.
- stop
PROGRAM :-
//Save as student.java
package MCA;
import java.util.*;
public class student
{int o,y,t=0,i;
double p;
String n;
int r[]=new int [50];
public student(int rollno,String
name)
{
y=rollno;
n=name;
System.out.println("Enter no of
subject");
Scanner s = new Scanner(System.in);
o=s.nextInt();
System.out.println("enter
marks");
for(i=0;i<o;i++)
{
System.out.println("Sub :"+(i+1));
r[i]=s.nextInt();
}
for(i=0;i<o;i++)
{
t=t+r[i];
}
System.out.println(" "+t);
p=(t*100)/(o*100.0);
}
public void display()
{
System.out.println("<========RESULT========>");
System.out.print("Name
:"+n);
System.out.println(" Roll No :"+y);
for(i=0;i<o;i++)
{
System.out.print("Sub :"+(i+1));
System.out.println(" "+r[i]);
}
System.out.print("Total
Marks: "+t);
System.out.print(" Percentage "+p+"%");
}
}
//save as e.java
import java.util.*;
import MCA.student;
class e
{
public static void main(String
[]args)
{
String a;int b;
Scanner s =new Scanner(System.in);
System.out.println("enter
Name");
a=s.nextLine();
System.out.println("enter Roll
no");
b=s.nextInt();
student t =new student(b,a);
t.display();
}
}
enter Name
Chetan
enter Roll no
65
Enter no of subject
2
enter marks
Sub :1
89
Sub :2
93
182
<========RESULT========>
Name :Chetan Roll No :65
Sub :1 89
Sub :2 93
Total Marks:182 Percentage 91.0%
Observations and learning:
Learn To create
user defined packages and there use in real world.
Conclusion:
By using package
in java we can solve the given problem
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