Java SE: Packages

Java Fundamentals

What is a Package in Java

1 Overview

📘 Design-patterns

In Java, a package is a collection of related classes and interfaces that provide a higher-level abstraction for organizing and modularizing your code.

Packages allow you to group similar classes and interfaces together, and to provide a convenient namespace for accessing those classes and interfaces from other parts of your program.

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When you create a new class or interface in Java, you can place it in a package by using the package keyword at the top of the file, followed by the name of the package.

Example.java

package com.example;

public class Example {
    // Class code goes here...
}

For example, the following code shows how to create a new class called Example and place it in the com.example package

By placing the Example class in the com.example package, you can access the class from other parts of your program by using the fully-qualified class name, which includes the package name as well as the class name.

For example, the following code shows how to use the Example class from within another class called Main:

Main.java

public class Main {
    public static void main(String[] args) {
        // Use fully-qualified class name to access Example class
        com.example.Example example = new com.example.Example();
    }
}

In this example, the Main class uses the com.example.Example class by specifying the fully-qualified class name, which includes the package name as well as the class name. This allows the Main class to access the Example class from within the com.example package.

2 Package in Java SE or Java EE is not similiar

Important

The package that a class is placed in can be an important factor in how the framework resolves requests. This is because the Spring Framework uses the package structure of a project to help determine the path of a request, and to map the request to the appropriate controller or handler.

For example, consider a Spring MVC application that contains a com.example.web package, which contains a HomeController class that is used to handle requests to the application’s home page. In this case, the HomeController class is placed in the com.example.web package, which means that the path of a request to the home page would include the package name as part of the URL.

For instance, if the application’s base URL is http://localhost:8080, then a request to the home page might have a URL like the following:

http://localhost:8080/com.example.web/home

In this case, the com.example.web package is part of the path that resolves the request to the HomeController class, which is responsible for handling the request and generating a response.

3 Conclusion

Overall, packages are an important concept in Java, and can help to improve the modularity, organization, and maintainability of your code. By grouping related classes and interfaces together into packages, you can provide a convenient namespace for accessing those classes and interfaces, and you can better manage the dependencies between different parts of your program.