Access Modifiers

About

Access modifiers in Java control the visibility of classes, methods, variables, and constructors. They determine who can access a particular member of a class.

Types of Access Modifiers

Modifier	Accessible Within Class	Accessible Within Package	Accessible in Subclasses	Accessible Outside Package
private	✅ Yes	❌ No	❌ No	❌ No
default (no modifier)	✅ Yes	✅ Yes	❌ No	❌ No
protected	✅ Yes	✅ Yes	✅ Yes	❌ No
public	✅ Yes	✅ Yes	✅ Yes	✅ Yes

1. Private Access Modifier (private)

Scope: Accessible only within the same class. Use case: Used for data hiding and encapsulation.

Example:

class Example {
    private int secretCode = 1234;  // Private variable

    private void displaySecret() {  // Private method
        System.out.println("Secret Code: " + secretCode);
    }

    public void show() {  // Public method to access private members
        displaySecret();
    }
}

public class Main {
    public static void main(String[] args) {
        Example obj = new Example();
        // obj.secretCode = 5678;  // Error: Cannot access private variable
        // obj.displaySecret();    // Error: Cannot access private method
        obj.show();  // Allowed: Indirect access through public method
        // Secret Code: 1234
    }
}

2. Default (No Modifier) Access (Package-Private)

Scope: Accessible within the same package only. Use case: Used when members should be shared within a package but not outside.

Example:

class PackageExample {
    int packageVariable = 42;  // Default access modifier

    void display() {  // Default method
        System.out.println("Package Variable: " + packageVariable);
    }
}

public class Main {
    public static void main(String[] args) {
        PackageExample obj = new PackageExample();
        obj.display();  // Allowed: Same package
    }
}

3. Protected Access Modifier (protected)

Scope: Accessible within the same package and in subclasses (even in different packages). Use case: Used for inheritance to allow controlled access to subclasses.

Example:

class Parent {
    protected String message = "Hello from Parent!";  // Protected variable
}

class Child extends Parent {
    void showMessage() {
        System.out.println(message);  // Allowed: Accessible in subclass
    }
}

public class Main {
    public static void main(String[] args) {
        Child child = new Child();
        child.showMessage();
        // Hello from Parent!
    }
}

4. Public Access Modifier (public)

Scope: Accessible everywhere (within and outside the package). Use case: Used when members should be fully accessible.

Example:

class PublicExample {
    public String message = "Public Access!";  // Public variable

    public void showMessage() {  // Public method
        System.out.println(message);
    }
}

public class Main {
    public static void main(String[] args) {
        PublicExample obj = new PublicExample();
        obj.showMessage();  // Allowed: Public access
        // Public Access!
    }
}

Access Modifier Usage with Classes

Modifier	Class	Method	Variable	Constructor
private	❌ Not allowed	✅ Yes	✅ Yes	✅ Yes
default	✅ Yes	✅ Yes	✅ Yes	✅ Yes
protected	❌ Not allowed	✅ Yes	✅ Yes	✅ Yes
public	✅ Yes	✅ Yes	✅ Yes	✅ Yes

Example:

// Allowed: Public class
public class Car {
    private String engine;  // Private variable
    protected int speed;    // Protected variable
    public String model;    // Public variable

    // Constructor
    public Car(String model, int speed) {
        this.model = model;
        this.speed = speed;
    }

    private void startEngine() {  // Private method
        System.out.println("Engine started!");
    }

    protected void accelerate() {  // Protected method
        System.out.println(model + " is accelerating.");
    }

    public void displayInfo() {  // Public method
        System.out.println("Car Model: " + model + ", Speed: " + speed);
    }
}

When to Use Which Access Modifier?

Use Case	Best Access Modifier
Hide internal implementation	private
Allow subclass access but hide from external classes	protected
Allow access within the same package	default (no modifier)
Make it accessible to everyone	public