Packages are used in Java, in order to avoid name conflicts and to control access of class, interfaces etc. Packages in Java are a way to encapsulate interfaces, Java classes and also subclasses. They are used for the following tasks –

1. Java Packages are used to prevent the naming conflicts which can occur between the classes.
2. Packages in Java make the searching and locating of classes or annotations much easier.
3. Java Packages provide access control to the classes.
4. Packages are used for data encapsulation.

Types of  packages in Java:

1)Built-in Packages in Java

Built-in Java packages are a part of Java API and it offers a variety of packages, list of java packages are –

• lang – Automatically imported and it contains language support classes.

• io – Contains classes for input and output operations.

• util – contains utility classes for implementing data structures.

• applet – This package contains classes that create applets

• awt – Contain classes that implement compounds for GUI.

• Swing-contains classes for making light-weighted user interfaces for desktop applications.

• net – This package contains classes that support networking operations.

• Sql-This package contains classes that support database operations.

 

2)User-defined Packages in Java

 

Java User creates these Java packages.

 

 

The first example of a java package:

 

package A;  

public class First

{  

public static void main(String args[])

{  

                        System.out.println(“First package”);  

            }

}

 

How to compile:            javac -d . First.java 

How to run:                     java  A.First

 

Accessing package from another  package

Using packagename.*

package pack1;  

public class A

{  

  public void msg()

{

System.out.println(“Hello package”);

}  

}

 

 

package pack2;  

import pack1.*;  

class B

{  

            public static void main(String args[])

{  

                        A obj = new A();  

                        obj.msg();  

            }  

}

 

 

Using packagename.classname

package P1;  

public class A

{  

public void msg()

{

System.out.println(“Hello Package”);

}  

}  

 

package P2;  

import P1.A;  

class B

{  

            public static void main(String args[])

{  

                        A obj = new A();  

                        obj.msg();  

            }  

}

Note: The second technique is used only when we know the exact name of a particular class otherwise the first technique is fine.