🌐 What are Access Modifiers?

Access modifiers control where a class, method, or field can be accessed from.
Java provides 4 levels of access:

Modifier	Access Scope
public	Accessible from everywhere (inside the class, package, subclasses, and outside packages)
protected	Accessible within the same package and also in subclasses, even if they are in different packages
default (no modifier)	Accessible within the same package only
private	Accessible only within the same class

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🔎 Detailed Explanation

1️⃣ public

• Most open access.
• Can be accessed from anywhere — inside the same class, other classes in the same package, and even classes in different packages.
• Suitable for APIs, public methods, constants.

public class Animal {
    public void eat() {
        System.out.println("Animal eating");
    }
}

✅ This eat() method can be called from any class, in any package.

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2️⃣ protected

• Accessible within:
  • Same package (like default).
  • Subclasses, even if the subclass is in a different package.
• Suitable for:
  • Methods intended for inheritance (but not for general use).

class Animal {
    protected void makeSound() {
        System.out.println("Animal sound");
    }
}

✅ A Dog subclass (even in a different package) can call makeSound(), but unrelated classes cannot.

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3️⃣ default (package-private)

• No keyword means default access.
• Accessible only within the same package.
• Suitable for:
  • Package-internal classes and helpers.

class Animal {
    void sleep() {
        System.out.println("Animal sleeping");
    }
}

✅ This sleep() method can only be called from other classes in the same package.

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4️⃣ private

• Most restrictive.
• Accessible only within the same class.
• Suitable for:
  • Internal fields, helper methods, or private logic you want to hide from others.

class Animal {
    private void breathe() {
        System.out.println("Animal breathing");
    }
}

✅ No class outside Animal can access breathe(), not even subclasses.

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📊 Quick Summary Table

Modifier	Same Class	Same Package	Subclass (Different Package)	Other Packages
public	✔️	✔️	✔️	✔️
protected	✔️	✔️	✔️	❌
default	✔️	✔️	❌	❌
private	✔️	❌	❌	❌

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🔥 Important Rules for Interviews

✅ Classes (top-level) can only be public or default — they cannot be private or protected.

✅ Inside a class (fields, methods, inner classes), you can use all 4 (public, protected, default, private).

✅ protected = package + inheritance — this is often misunderstood!

✅ default = package-private — this is the actual technical name.

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📚 Example for All Modifiers in One File

public class Animal {
    public String name;          // Accessible everywhere
    protected int age;            // Accessible in package + subclasses
    String type;                   // Package-private (default)
    private String secret;         // Accessible only within Animal class

    public void eat() { System.out.println("Eating"); }          // Public
    protected void makeSound() { System.out.println("Sound"); }  // Protected
    void sleep() { System.out.println("Sleeping"); }             // Default
    private void breathe() { System.out.println("Breathing"); }  // Private
}

🎯 Final Pro Tip for Interviews

✅ If you need to explain best practices, say:

• public: for public APIs, library methods.
• protected: for methods meant for extension (subclasses).
• default: for package-internal helpers.
• private: for strict internal logic (encapsulation).

✅ Inheritance trick: protected is more open than default — protected works even across packages, but only for subclasses.