Java Packages and Imports

A package is a folder of related classes. Packages keep big projects organized and avoid name clashes: two different classes can both be named Date if they are in different packages.

Built in packages

Package	Contains
java.lang	Core classes (String, Math, System). Imported automatically
java.util	Collections, Scanner, Random
java.io, java.nio.file	Files and streams
java.time	Dates and times
java.net	Networking

import

import java.util.ArrayList;
import java.util.List;
import java.time.LocalDate;

public class Main {
    public static void main(String[] args) {
        List<String> names = new ArrayList<>();
        names.add("Riya");
        System.out.println(names);
        System.out.println(LocalDate.of(2026, 1, 15));
    }
}

import java.util.*; imports all the classes of a package. It is fine, but many teams prefer to import each class, so it is clear where a name comes from.

Create your own package

The package statement must be the first line, and the folders must have the same name. We make a small project with two files:

package com.shop;

public class Product {
    private final String name;
    private final double price;

    public Product(String name, double price) {
        this.name = name;
        this.price = price;
    }

    public String describe() {
        return name + " costs " + price;
    }
}

import com.shop.Product;

public class Main {
    public static void main(String[] args) {
        Product p = new Product("Book", 250);
        System.out.println(p.describe());
    }
}

javac -d out puts the compiled classes in the out folder, with the package folders. -cp out tells Java where to look for the classes (the class path).

Static import

import static java.lang.Math.*;

public class Static {
    public static void main(String[] args) {
        System.out.println(sqrt(144) + " " + max(3, 8) + " " + PI);
    }
}

Name clash

When two classes have the same name, use the full name:

public class Clash {
    public static void main(String[] args) {
        java.util.Date a = new java.util.Date(0);
        java.sql.Date b = new java.sql.Date(0);
        System.out.println(a.getClass().getName());
        System.out.println(b.getClass().getName());
    }
}

Naming convention

Package names are in small letters, and start with a reversed domain name: com.tutorialsclass.shop. This makes them unique in the world.

Modules (short note)

Since Java 9 there is also the module system (module-info.java) for very big applications. Most beginners and many projects do not need it.

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