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Packages in Java

16th October 2023

A set of classes and interfaces grouped together are known as Packages in Java

Benefits

  • Organize grioup of classes into single API Unit
  • auto control naming conflicts
  • easy access protection
  • 2 access levels: Protected, Default

Java Package Subpackage Class units

Other 2 major types: BuiltIn , UserDefined

Java.awt.event:

  • Java: Package
  • awt: sub package
  • event: class

BuiltIn

come along with JDK use import statement

package Example;
import java.util.ArrayList;

class buildinpackage{
    psvm{
        // define array, insert elements, print array
    }
}

How to access package from another package?

  1. import package.* (available for both BI and UD)
  2. import package.classname
  3. some fully qualified name, without import

fully qualified like:

class myarray implements java.util.ArrayList{
    // something
}

makes only the declared class of the package accessible adv when two packages have same class name

Creating a Package

  • use package command as the starting statement, like package Example
  • further define all necessary classes

creating a class inside a package while importing another package is also valid

to define a subpackage, modify package command acc, like package ExamplePackage.multiply

Private Package: can only access private modifier within the package Protected Package: can only access directly from the class and thru classes from child class. They make use of the inheritance concept

Public: can be accessed anywhere (within class and outside class)

Access Modifier Access in Class Access in Package Access outside package using subclass Access directly outside class
Private Y N N N
Default Y Y N N
Protected Y Y Y N
Public Y Y Y Y