Java's Customizable Module System: A Look at User-Defined Packages
Creating a user-defined package in Java is an essential skill for organizing classes and making them easier to find and use. Here's a straightforward guide to help you create and use a user-defined Java package.
- Create the package and add classes
At the beginning of your Java source file, declare the package name using the keyword followed by the package name (usually in lowercase). Then, write your class inside this file. For example:
```java package example;
public class Geeks { public void show() { System.out.println("Hello geeks!! How are you?"); }
} ```
- Compile the class
Compile the file from the command line. The compiled files will be placed in a folder structure that matches the package name. For example:
- Use the package in another Java program
Import the package and use its class functionality.
```java import example.Geeks;
public class Test { public static void main(String[] args) { Geeks obj = new Geeks(); obj.show(); } } ```
- Run the program
Run the program using the command and specify the classpath if needed.
Key points:
- The package declaration should always be the first statement.
- Classes inside a package are organized in a folder structure that matches the package name.
- Import the package to use it in other classes.
- Package names typically use all lowercase names for clarity.
This process can be summarized as follows:
| Step | Description | Example | |--------------------------|----------------------------------------------|----------------------------------| | 1. Create package | Declare package at top of Java source file. | | | 2. Compile | Compile class with package folder structure. | | | 3. Import & use | Import package in another class and use. | | | 4. Run | Run the program using command. | |
These steps and example are based on Java package creation guides from GeeksforGeeks and other educational resources[1][3][5].
It's worth noting that if you omit the package statement in a class, the class names will be put into the default package, which has no name. A class in Java can only have one package declaration.
The output of both programs will show the greeting message "Hello geeks!! How are you?". Built-in packages, such as java.io. and java.lang., are already defined packages provided by Java.
In a Java program, you can create a new user-defined package using the 'package' keyword, followed by the package name, to organize your classes. This technology allows for easier management and accessibility of your classes within the Java environment.
Moreover, when you compile a class, the compiled files will be placed in a folder structure that reflects the package name, making it easier to use the class in other Java programs through the 'import' statement.
