📦 Java Packages, Access Modifiers, and the static Keyword

🔖 Introduction

In Java, organizing your code and controlling access is essential as your project grows. This lesson introduces:

• Packages – organize classes logically
• Access Modifiers – control who can use what
• The static keyword – shared methods and variables

Let’s break them down with examples 👇

📁 Java Packages – Organizing Classes

---

✅ What is a Package?

A package is a namespace that groups related classes and interfaces. Think of it as a folder in your project.

package myapp.utils;

public class Helper {
    public static void sayHi() {
        System.out.println("Hi from Helper!");
    }
}

📌 Using a Class from Another Package

import myapp.utils.Helper;

public class Main {
    public static void main(String[] args) {
        Helper.sayHi();
    }
}

💡 Why Use Packages?

• Avoid class name conflicts
• Organize files logically
• Control access using modifiers

🔐 Access Modifiers in Java

Access modifiers define who can access a class, method, or variable.

Modifier	Accessible within Class	Package	Subclass	Everywhere
private	✅	❌	❌	❌
(default)	✅	✅	❌	❌
protected	✅	✅	✅	❌
public	✅	✅	✅	✅

🔐 Example of All Modifiers

public class Example {
    private int secret = 123;
    int defaultValue = 10;         // package-private
    protected int inherited = 50;
    public int visibleEverywhere = 100;
}

⚙️ The static Keyword – Shared Across Objects

---

✅ What is static?

• Belongs to the class, not instances
• Memory is allocated once
• Accessed using the class name

---

🔹 Static Variable Example

class Counter {
    static int count = 0;

    Counter() {
        count++;
    }
}

Usage:

public class Test {
    public static void main(String[] args) {
        new Counter();
        new Counter();
        System.out.println(Counter.count);  // 2
    }
}

🔸 Static Method Example

class MathUtils {
    static int square(int x) {
        return x * x;
    }
}

Usage:

System.out.println(MathUtils.square(5));  // 25

💡 Quick Tip

You can access static methods/variables without creating an object.

🧪 Challenge: Static ID Generator

class Employee {
    static int nextId = 1;
    int id;

    Employee() {
        id = nextId++;
    }
}

public class Company {
    public static void main(String[] args) {
        Employee e1 = new Employee();
        Employee e2 = new Employee();
        System.out.println(e1.id); // 1
        System.out.println(e2.id); // 2
    }
}

✅ What You Learned

• Packages group related classes
• Access Modifiers control visibility
• static members belong to the class, not the instance