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.

We have the following two packages in Java:

• Built-in packages
• User-defined packages

Built-in Packages

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.

How to declare a user-defined package in Java

Before beginning, let us see the syntax for package declaration in Java. The following must be the first line in the file:

package packageName;

How to import a user-defined package in Java

Use import packageName.ClassName; to access classes from other packages.

Example

Create a file in the 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:

Steps to Create User-Defined Packages in Java (IntelliJ IDEA)

1. Create a New Project

• Open IntelliJ IDEA → File → New → Project.
• Select Java and configure the JDK.
• Name your project (e.g., PackageDemo).

2. Create a Package

• In the Project tool window, right-click on the src folder.
• Select New → Package.
• Enter a name (e.g., mypackage).IntelliJ will create a folder src/mypackage.

3. Add a Class to the Package

• Right-click on the package → New → Java Class.
• Name it (e.g., HelloWorld).
• At the top of the file, IntelliJ automatically adds:

package mypackage;

public class HelloWorld {
    public void displayMessage() {
        System.out.println("Hello from mypackage!");
    }
}

4. Use the Package in Another Class

• Create another class in the src folder (outside the package or in another package).
• Import the class:

import mypackage.HelloWorld;

public class Main {
    public static void main(String[] args) {
        HelloWorld obj = new HelloWorld();
        obj.displayMessage();
    }
}

5. Run the Program

• Right-click on Main.java → Run ‘Main.main()’.
• Output:

Hello from mypackage!

6. Folder Structure in IntelliJ

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