What is Java Package?
A package is a collection of related classes and interfaces,etc.,
Each package in Java has its unique name and organizes your classes and interfaces into a folder structure and make it easy to locate and use them.
More importantly, it helps improve re-usability.
Types of Package:
- Built-in Package
- User-defined-package
What is Built-in Package?
These packages consists of a large number of classes which are a part of Java API.
For e.g, we have used java.io package previously which contain classes to support input / output operations in Java.
Similarly, there are other packages which provides different functionality.
Package Name | |
---|---|
java.lang | Contains language support classes ( for e.g classes which defines primitive data types, math operations, threads,exceptions,etc.) . This package is automatically imported. |
java.io | Contains classes for supporting input / output operations. |
java.util | Contains utility classes which implement data structures like Linked List, Hash Table, Dictionary, etc and support for Date / Time operations. |
java.applet | Contains classes for creating Applets. |
java.awt | Contains classes for implementing the components of graphical user interface ( like buttons, menus,list, etc. ). |
java.net | Contains classes for supporting networking operations.They include classes for communicating with local computers as well as with internet servers. |
What is User-defined-package?
User-defined-package is defined by programmers to bundle group of related classes,interfaces,etc.,
How to Creat a package?
Creating a package in java is quite easy. Simply include a package command followed by name of the package as the first statement in java source file.
Syntax
package packagename; Example:package mypack;
The above statement create a package called mypack.
Example
package mypack; public class A{ public void show(){ System.out.println("Show method"); } }
What is import keyword?
import keyword is used to import built-in and user-defined packages into your java source file.
So that your class can refer to a class that is in another package by directly using its name.
There are 2 different ways to refer to class that is present in different package.
How to import the only class you want to use?
Example
package Demo; import java.util.Date; class MyDate extends Date{ //statements }
How to import all the classes from the particular package?
Example
package Demo; import java.util.*; class MyDate extends Date{ //statement; }
Where the import statement is kept in java?
import statement is kept after the package statement.
Example
package Demo; import java.util.*;
But if you are not creating any package then import statement will be the first statement of your java source file.
Example
package mypack; public class A{ public void show(){ System.out.println("Show method"); } } package demo; import mypack.A; public class Hello{ public static void main(String args[]){ A a=new A(); a.show(); System.out.println("show method from A class"); } }
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