06 Aug Java Packages

A Package in Java, as the name suggests, groups related types i.e., it can be a group of related classes or related interfaces, etc. We already have built-in packages in Java, but we can also create our own packages to group related classes.

The following are some built-in Java packages:

java.util
java.io
java.lang
java.time
java.math

To import the entire package, use the import keyword:

import java.util.* ;
import java.io.* ;
import java.lang.* ;
import java.time.* ;
import java.math.* ;

User-defined Package

Let us now learn how to create a user-defined package in Java. Create a file in D: drive:

The package keyword will be used in our Java program to use the package:

package amitpackage;

Let us create Demo.java:

package amitpackage;

class Demo { 
  public static void main(String[] args) { 
    System.out.println("Our Demo class..."); 
  } 
}

Now, compile the file Demo.java:

D:\ > javac Demo.java

Compile the package:

D:\ > javac -d . Demo.java

The screenshot displays the same command:

Now, a new folder amitpackage will get created. Here’s the screenshot:

Run the Demo.java:

D:\ > java amitpackage.Demo

The above file will run successfully and now a class file will be visible in the amitpackage:

Also, the output “Our Demo class” will be visible on cmd:

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