25. Package In Java


✔ JAVA CHAPTERS:-

1. Introduction to Java
2. Features of Java
3. Java Virtual Machine
4. D/F B/W JVM, JRE, JDK
5. Java Data Types
6. Java Programs
7. Setting Java Path
8. OOPs Concepts
9. Object & Class In Java
10. OOPs Continued
11. Encapsulation & Polymorphism
12. Method Overloading
13. Method Overriding
14. Dynamic Method Dispatch
15. Association In Java
16. Inheritance in Java
17. Aggregation in java
18. Command Line Argument
19. Execute Command Line
20. Read Input From Command Line
21. Abstract Class In Java
22. Interface in Java
23. Cutom Marker Interface
24. Constructor In Java
25. Package in Java
26. Acess Modifier In Java
27. Static Import In Java
28. Package Class In Java
29. This Keyword
30. Instance Intializer Block
31. Super Keyword
32. Static Keyword
33. Final Keyword



Constructor In Java: Previous                                                           Next: Access Modifier in Java

Package In Java

Package:

Package is a namespace that is used to group logically related classes and interfaces.

Advantages/Benefits of package in java:

  1. 1. Package provides unique namespace.
  2. 2. Package provides access protection.
  3. 3. Package provides grouping of logically related classes and interfaces so easy to maintain.

How to create a package:

A package is created with package keyword.

Example:

PackageExample1.java
package test;
/**
 * This program is used to show simple use of package.
 * @author javatutorialpoint
 */
public class PackageExample1 {
        public static void main(String args[]){
               System.out.println("This is first package example.");
        }
}

Output:

This is first package example.

 How to access package from outside the package:

  1. 1. Using import keyword.
  2. a. Import packagename.*;
All classes and interface will be accessible but not of subpackages.
  1. b. Import packagename.classname;
Only specific class is accessible.
  1. 2. Using full qualified name.
Specific class will be accessible and no need to import but everywhere it is used fully qualified name is needed.

Example of import packagename.*

Display.java
package com.javawithease.display;
/**
 * This class is used to display entered text.
 * @author javatutorialpoint
 */
public class Display {
        public void displayText(String text){
               System.out.println(text);
        }
}
Test.java
package test;
import display.*;
/**
 * This class is used to show package use with import packagename.*.
 * @author javatutorialpoint
 */
public class Test {
       public static void main(String args[]){
               Display display = new Display();
               display.displayText("Hello java.");
        }
}

Output:

Hello java.

Example of import packagename.classname

Display.java
package com.javawithease.display;
/**
 * This class is used to display entered text.
 * @author javatutorialpoint
 */
public class Display {
       public void displayText(String text){
              System.out.println(text);
       }
}
Test.java
package test;
import display.Display;
/**
 * This class is used to show package using import packagename.className.
 * @author javatutorialpoint
 */
public class Test {
       public static void main(String args[]){
              Display display = new Display();
              display.displayText("Hello java.");
       }
}

Output:

Hello java.

Example of using full qualified name

Display.java
package display;
/**
 * This class is used to display entered text.
 * @author javatutorialpoint
 */
public class Display {
       public void displayText(String text){
              System.out.println(text);
       }
}
Test.java
package test;
/**
 * This class is used to show package using full qualified name.
 * @author javatutorialpoint
 */
public class Test {
       public static void main(String args[]){
              display.Display display =
                             new display.Display();
              display.displayText("Hello java.");
       }
}

Output:

Hello java.

Subpackage:

A package inside a package is known as subpackage.

Example:

Display.java
package com.javawithease.display;
/**
 * This class is used to display entered text.
 * @author javatutorialpoint
 */
public class Display {
       public void displayText(String text){
              System.out.println(text);
       }
}
Test.java
package com.javawithease.test;
import com.javawithease.display.*;
/**
 * This class is used to show sub package using import.
 * @author javatutorialpoint
 */
public class Test {
       public static void main(String args[]){
              Display display =
                       new Display();
              display.displayText("Hello java.");
       }
}

Output:

Hello java.

 Note: If a package is import, all classes and interface will be accessible of that package but not of subpackages. So subpackage also be import to access classes and interfaces of subpackage.

 Example:

Display.java
package com.javawithease.display;
/**
 * This class is used to display entered text.
 * @author javatutorialpoint
 */
public class Display {
       public void displayText(String text){
              System.out.println(text);
       }
}
Test.java
package com.javawithease.test;
import com.javawithease.*;
/**
 * This class is used to show sub package classes
 * will not import if package is imported.
 * @author javatutorialpoint
 */
public class Test {
       public static void main(String args[]){
               //Error
               Display display = new Display();
               display.displayText("Hello java.");
       }
}

Output:

Exception in thread "main" java.lang.Error: 
Unresolved compilation problems:
Display cannot be resolved to a type
Display cannot be resolved to a type
at com.javawithease.test.Test.main(Test.java:13)

Constructor In Java: Previous                                                           Next: Access Modifier In Java