Explain packages in Java

In Java classes and interfaces related to each other are grouped under a package. Package is nothing but a directory storing classes and interfaces of a particular concept. For example, all the classes and interfaces related to input and output operations are stored in java.io package.

Creating a package

You can group required classes and interfaces under one package just by declaring the package at the top of the Class/Interface (file) using the keyword package as −

Example

package com.tutorialspoint.mypackage;
public class Sample {
   public void demo() {
      System.out.println("This is a method of the sample class");
   }
   public static void main(String args[]) {
      System.out.println("Hello how are you......");
   }
}

Compiling a program with a package

Unlike other programs to compile a program with a package, you need to use the –d option of the javac command specifying the destination path where you need to create the package.

javac –d . Sample.java

If you haven’t mentioned the destination path the package will be created in the current directory.

Executing the .class file created with in a package

To execute the byte code within a file you need to specify the absolute class name (name along with the package) as −

java com.tutorialspoint.mypackage.Sample
Hello how are you......

Accessing the contents of a package

To access the classes/interfaces that are grouped under a package, you need to add the location of the package in the classpath variable (or make sure the package is in the current directory) and import the class/interface of it using the import keyword.

Example

import com.tutorialspoint.mypackage.Sample;
public class Test {
   public static void main(String args[]) {
      Sample obj = new Sample();
      obj.demo();
   }
}

Output

This is a method of the sample class