Imagine you are building a large Java application with multiple teams working on different modules. Without proper organization, managing code would be chaotic. Just like departments in a company, user-defined packages allow you to logically separate and manage your code.
This organization not only brings clarity but also enhances modularity, reusability, and scalability—key principles in software engineering.
User-defined packages in Java are packages that developers create to logically group related classes, interfaces, and sub-packages.
package keyword as the first statement in your Java file.-d option to specify the destination directory.import statement.Best Practice: Use your organization’s reversed domain name for naming packages (e.g., com.example.utils) to avoid name conflicts in collaborative environments.
// File: mypack/Message.java
package mypack;
public class Message {
public void greet() {
System.out.println("Hello from my user-defined package!");
}
}
// File: Main.java
import mypack.Message;
public class Main {
public static void main(String[] args) {
Message m = new Message();
m.greet();
}
}
To compile and run:
javac -d . mypack/Message.java
javac Main.java
java MainDivide functionality into different packages like utils, services, models, etc., in enterprise software.
Create custom libraries with grouped classes and share them across multiple projects or teams.
Use packages with default access modifiers to restrict class usage within specific boundaries.
Use the package keyword at the top of the class file, compile using javac -d, and import it where needed.
-d option during compilation?The -d option specifies the destination directory where the package folders and class files should be created.
No, a Java class can belong to only one package declared at the top of the file using the package keyword.
It allows teams to work on different packages independently, avoids class name collisions, and enables controlled access between modules.