Packages in Java Import Built in Packages

Creating a Package

A Java package creates a namespace and an access boundary. Its declaration, directory layout, imports, qualified names, and module or build configuration must agree.

In larger Java applications, packages become architecture boundaries. Keep controller, service, model, repository, and utility classes in clear packages so imports explain the project structure instead of becoming random file locations.

Keep package declarations, source directories, imports, qualified names, and access modifiers aligned so namespace boundaries are visible in code and builds.

The package statement must be the first non-comment line in a Java file. The folder path should match the package name.

Package Declaration

// File: com/tutorialslogic/app/Main.java
package com.tutorialslogic.app;

public class Main {
    public static void main(String[] args) {
        System.out.println("Package demo");
    }
}

Importing Classes

Use import to refer to classes from other packages by simple name. java.lang is imported automatically.

Import Example

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

public class ImportDemo {
    public static void main(String[] args) {
        List<String> names = new ArrayList<>();
        names.add("Java");
        System.out.println(LocalDate.now());
    }
}

Compile and Run Package Classes

When using packages from the command line, compile from the source root and run using the fully qualified class name.

Command Line Package Run

javac -d out src/com/tutorialslogic/app/Main.java
java -cp out com.tutorialslogic.app.Main

-d tells javac where to place compiled class files.
-cp tells java where to find compiled classes.

Package and Import Rules

The package statement must be the first non-comment statement in a Java file. Imports let you use classes from other packages without writing the full name every time.

Folder structure should match package names.
java.lang is imported automatically.
Avoid the default package in real projects.
Package-private members are visible only inside the same package.

Organizing Java classes with packages and imports

Packages group related Java classes under a namespace. They prevent name conflicts, make large projects easier to browse, and show which part of the application a class belongs to. A class named UserService inside com.shop.users communicates much more than a loose UserService file in a flat folder.

Imports do not copy code into the file. They simply let the compiler resolve a class name without writing the full package every time. Built-in packages such as java.util and java.time are used constantly, while custom packages are created to match modules such as controllers, services, models, and repositories.

Put the package declaration as the first non-comment line.
Match folder structure with package names.
Import only the classes you need or use fully qualified names for rare conflicts.
Use lowercase package names to follow Java convention.

Custom package with a built-in import

package com.school.reports;

import java.time.LocalDate;

public class AttendanceReport {
    public String heading() {
        return "Attendance report for " + LocalDate.now();
    }
}

Before you move on