Defining Packages in java
In java, a package is a container of classes, interfaces, and sub-packages. We may think of it as a folder in a file directory.
We use the packages to avoid naming conflicts and to organize project-related classes, interfaces, and sub-packages into a bundle.
In java, the packages have divided into two types.
- Built-in Packages
- User-defined Packages
Built-in Packages
The built-in packages are the packages from java API. The Java API is a library of pre-defined classes, interfaces, and sub-packages. The built-in packages were included in the JDK.
There are many built-in packages in java, few of them are as java, lang, io, util, awt, javax, swing, net, sql, etc.
We need to import the built-in packages to use them in our program. To import a package, we use the import statement.
User-defined Packages
The user-defined packages are the packages created by the user. User is free to create their own packages.
Definig a Package in java
We use the package keyword to create or define a package in java programming language.
package packageName;
🔔 The package statement must be the first statement in the program.
🔔 The package name must be a single word.
🔔 The package name must use Camel case notation.
Let's consider the following code to create a user-defined package myPackage.
package myPackage;
public class DefiningPackage {
public static void main(String[] args) {
System.out.println("This class belongs to myPackage.");
}
}
Now, save the above code in a file DefiningPackage.java, and compile it using the following command.
javac -d . DefiningPackage.java
The above command creates a directory with the package name myPackage, and the DefiningPackage.class is saved into it.
Run the program use the following command.
java myPackage.DefiningPackage
🔔 When we use IDE like Eclipse, Netbeans, etc. the package structure is created automatically.