Java Access Modifiers and Package-Level Access

 

🔐 Java Access Modifiers and Package-Level Access

Java provides four access levels:

Access Modifier	Class	Package	Subclass	World (outside package)
public	✅	✅	✅	✅
protected	✅	✅	✅	❌
(default) no modifier	✅	✅	❌	❌
private	✅	❌	❌	❌

📦 How It Works in Packages

1. public

• Accessible from any class in any package.

• Typically used when a class or method needs to be globally available.

Example:

package mypack;

public class A {
    public void show() {
        System.out.println("Public method");
    }
}

2. protected

• Accessible within the same package and also by subclasses in other packages.

• Often used in inheritance scenarios.

Example:

package mypack;

public class A {
    protected void display() {
        System.out.println("Protected method");
    }
}

package otherpack;

import mypack.A;

class B extends A {
    void callDisplay() {
        display();  // Valid because B is a subclass of A
    }
}

3. Default (no modifier)

• Package-private: accessible only within the same package.

• Used when you want a class or method to be hidden from other packages.

Example:

package mypack;

class A { // default class
    void show() {
        System.out.println("Default access method");
    }
}

• This class A cannot be accessed from a class in a different package.

4. private

• Accessible only within the same class.

• Not accessible from other classes even in the same package.

• Commonly used for data hiding.

Example:

package mypack;

public class A {
    private int x = 5;

    private void display() {
        System.out.println("Private data: " + x);
    }
}

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🧠 Key Points for Instructors

• Default access is often misunderstood — remind students it's only package-level.

• protected offers the most nuanced behavior, useful when mixing packages and inheritance.

• Best practice: make class members private, then expose functionality using public or protected methods if needed.

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✅ Summary Table

Modifier	Accessible in Same Class	Same Package	Subclass (other package)	Unrelated Class (other package)
public	✅	✅	✅	✅
protected	✅	✅	✅	❌
default	✅	✅	❌	❌
private	✅	❌	❌	❌