Java packages

java's package/module system is different from both python/cpp. Modules are assigned to packages using a statement in code, which does not necessarily have anything to do with the organization of your code within your filesystem.

Defining Packages

In this example, despite HelloWorld 1/2 residing in the same directory, one is assigned to the package beginner.examples and the other is assigned to expert.examples.

src/
    HelloWorld_1.java
    HelloWorld_2.java

package beginner.examples

class HelloWorld_1 {
    static void main(String[] args){ System.out.println("Hello World"); }
}

package expert.examples

class HelloWorld_2 {
    static void main(String[] args){ System.out.println("Hello World"); }
}

Imports

imports work by importing the objects from a class directly into the current namespace.

import beginner.examples.HelloWorld_1   // imports all classes defined within 'HelloWorld_1.java'
import beginner.examples.*              // imports all classes defined within modules in the package 'beginner.examples'

Static Imports

Static imports allow you to access static methods like functions directly, without any reference to their objects. Java docs caution to use this sparingly.

// MyClass.java

class MyClass
{
    static void print_hi() { System.out.println("hi") };
}

// App.java

import static MyClass;

class App
{
    public static void main()
    {
        print_hi();   // <-- not MyClass.print_hi()
    }
}