Java - Package

What is a package?

A package is a kind of directory that contains a group of related classes and interfaces. Packages hides its class and interfaces in a separate directory. Java has many such packages it its library. If you want to use a classes, you  have to import it into your program. If you want to use a method, then you have to import the corresponding class or interface.

A group of package is called library. Any class and interface inside a package is reusable.When a package is imported, its sub-packages are not automatically imported into a program. A separate import statement should be written to for every package or sub-package.

Java library

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Packages

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Classless and interfaces

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methods

There are two different types of packages.

1. build-in

2. User defined 

Build -in Packages

Build -in packages are already available in Java. These packages provide all necessary classes, interfaces and methods to perform tasks. Some important packages are:

java.lang:   This package has primary classes and interfaces for developing a basic Java program.

java.util: It has many useful collections. Date, time operations, victors... 

java.awt: awt stands for Abstract Window Toolkit.This package is useful for developing GUI-color, paintings, images etc. It consists one important sub-package java.awt.event. It provides actions like select radio button, menu etc.

javax.swing: Helpful for GUI. It is an extended package of java,awt(package developed from another package by adding new features). 'x' represents it as an extended package.

java.net: Useful for authentication for network, creating sockets, to establish communication between client-server.

java.applet: Related to Java applets.

java.text: It contains two important classes. 'DateFormat' is to format date and time. 'NumberFormat' is to format numeric values.

java.sql: Helps to connects to the database like oracle, retrieve and use data in Java program.

User-Defined Package: 

Package created by user. User defined package can be used exactly same way as the build-in package. 

The keyword to create a package is package.