Understanding Access Modifiers in Java: A Comprehensive Guide

Introduction ………………………………………………….1
Table of Access Modifiers ……………5
Public Access Modifier …………………….7
Default Access Modifier ……………….12
Protected Access Modifier …………..16
Private Access Modifier …………………….20
Access Modifiers and Inheritance..24
Conclusion ………………………………………………………28

Introduction

In the realm of Java programming, access modifiers play a pivotal role in defining the visibility and accessibility of classes, methods, and variables. Understanding these modifiers is essential for building robust and maintainable applications. This guide delves into the four primary access modifiers in Java—public, default, protected, and private—exploring their functionalities, use-cases, and implications in both non-inherited and inherited class scenarios.

Access modifiers not only enforce encapsulation but also enhance security by restricting unauthorized access to sensitive components of your code. Whether you’re a beginner or a developer with basic knowledge, mastering access modifiers will empower you to design cleaner and more efficient Java programs.

Table of Access Modifiers

Access Modifier	Class	Package	Subclass	World
Public	Yes	Yes	Yes	Yes
Protected	Yes	Yes	Yes	No
Default	Yes	Yes	No	No
Private	Yes	No	No	No

Table 1: Access Modifier Visibility Matrix

Public Access Modifier

Overview

The public access modifier is the most permissive modifier in Java. When a class, method, or variable is declared as public, it becomes accessible from anywhere—within the same package and from any other package.

Syntax and Usage

package org.studyeasy;

public class Other {
    public int x = 10;
    public String message() {
        return "Hello from the public method!";
    }
}

package org.studyeasy;

public class Other {

public int x = 10;

public String message() {

return "Hello from the public method!";

}

Key Concepts

Visibility: Accessible from all classes, regardless of the package.
Use-Case: Ideal for classes and methods that need to be accessed universally, such as utility classes or APIs.

Example Explained

In the above example, the Other class and its members x and message are declared as public. This means they can be accessed from any other class, even those in different packages.

package org.studyeasy;

public class Main {
    public static void main(String[] args) {
        Other other = new Other();
        System.out.println(other.x); // Outputs: 10
        System.out.println(other.message()); // Outputs: Hello from the public method!
    }
}

package org.studyeasy;

public class Main {

public static void main(String[] args) {

Other other = new Other();

System.out.println(other.x); // Outputs: 10

System.out.println(other.message()); // Outputs: Hello from the public method!

}

Output:

10
Hello from the public method!

1 2	10 Hello from the public method!

Default Access Modifier

Overview

When no access modifier is specified, Java applies the default access level, also known as package-private. Members with default access are accessible only within the same package.

Syntax and Usage

package org.studyeasy;

class Other {
    int x = 10;
    String message() {
        return "Hello from the default method!";
    }
}

package org.studyeasy;

class Other {

int x = 10;

String message() {

return "Hello from the default method!";

}

Key Concepts

Visibility: Accessible only within classes that reside in the same package.
Use-Case: Suitable for classes and members that should not be exposed outside their package, promoting encapsulation.

Example Explained

In this example, the Other class and its members x and message have default access. They cannot be accessed from classes outside the org.studyeasy package.

package org.anotherpackage;

import org.studyeasy.Other;

public class Main {
    public static void main(String[] args) {
        Other other = new Other(); // Compilation Error: Other is not public in org.studyeasy
    }
}

package org.anotherpackage;

import org.studyeasy.Other;

public class Main {

public static void main(String[] args) {

Other other = new Other(); // Compilation Error: Other is not public in org.studyeasy

}

Error:

Cannot access class Other from package org.anotherpackage

1	Cannot access class Other from package org.anotherpackage

Protected Access Modifier

Overview

The protected access modifier strikes a balance between public and default. Protected members are accessible within their own package and also in subclasses residing in different packages.

Syntax and Usage

package org.studyeasy;

public class Other {
    protected int x = 10;
    protected String message() {
        return "Hello from the protected method!";
    }
}

package org.studyeasy;

public class Other {

protected int x = 10;

protected String message() {

return "Hello from the protected method!";

}

Key Concepts

Visibility: Accessible within the same package and in subclasses across different packages.
Use-Case: Ideal for methods and variables that should be accessible to subclasses while restricting access from other classes.

Example Explained

package org.studyeasy;

public class Main {
    public static void main(String[] args) {
        Other other = new Other();
        System.out.println(other.x); // Outputs: 10
        System.out.println(other.message()); // Outputs: Hello from the protected method!
    }
}

package org.studyeasy;

public class Main {

public static void main(String[] args) {

Other other = new Other();

System.out.println(other.x); // Outputs: 10

System.out.println(other.message()); // Outputs: Hello from the protected method!

}

Output:

10
Hello from the protected method!

1 2	10 Hello from the protected method!

Subclass in Different Package:

package org.anotherpackage;

import org.studyeasy.Other;

public class SubClass extends Other {
    public void display() {
        System.out.println(x); // Accessible due to protected access
        System.out.println(message()); // Accessible due to protected access
    }
}

package org.anotherpackage;

import org.studyeasy.Other;

public class SubClass extends Other {

public void display() {

System.out.println(x); // Accessible due to protected access

System.out.println(message()); // Accessible due to protected access

}

Private Access Modifier

Overview

The private access modifier is the most restrictive. Private members are accessible only within the class they are declared in, ensuring complete encapsulation.

Syntax and Usage

package org.studyeasy;

public class Other {
    private int x = 10;
    private String message() {
        return "Hello from the private method!";
    }
    
    public String getMessage() {
        return message(); // Accessing private method within the class
    }
}

package org.studyeasy;

public class Other {

private int x = 10;

private String message() {

return "Hello from the private method!";

}

public String getMessage() {

return message(); // Accessing private method within the class

}

Key Concepts

Visibility: Accessible only within the declaring class.
Use-Case: Best for sensitive variables and methods that should not be exposed or modified directly from outside the class.

Example Explained

Attempting to access private members from another class results in errors.

package org.studyeasy;

public class Main {
    public static void main(String[] args) {
        Other other = new Other();
        System.out.println(other.x); // Compilation Error: x has private access
        System.out.println(other.message()); // Compilation Error: message() has private access
        System.out.println(other.getMessage()); // Outputs: Hello from the private method!
    }
}

package org.studyeasy;

public class Main {

public static void main(String[] args) {

Other other = new Other();

System.out.println(other.x); // Compilation Error: x has private access

System.out.println(other.message()); // Compilation Error: message() has private access

System.out.println(other.getMessage()); // Outputs: Hello from the private method!

}

Error:

x has private access in org.studyeasy.Other
message() has private access in org.studyeasy.Other

1 2	x has private access in org.studyeasy.Other message() has private access in org.studyeasy.Other

Output for getMessage():

Hello from the private method!

1	Hello from the private method!

Access Modifiers and Inheritance

Overview

Access modifiers significantly influence how inheritance behaves in Java. When a subclass inherits from a superclass, the accessibility of superclass members in the subclass depends on their access modifiers.

Public and Protected in Inheritance

Public Members: Inherited and accessible in the subclass without restrictions.
Protected Members: Inherited and accessible in the subclass, even if the subclass is in a different package.

Default and Private in Inheritance

Default Members: Inherited only if the subclass is in the same package.
Private Members: Not inherited; inaccessible in the subclass.

Example Explained

package org.studyeasy;

public class Parent {
    public int publicVar = 1;
    protected int protectedVar = 2;
    int defaultVar = 3;
    private int privateVar = 4;
}

package org.anotherpackage;

import org.studyeasy.Parent;

public class Child extends Parent {
    public void display() {
        System.out.println(publicVar); // Accessible
        System.out.println(protectedVar); // Accessible
        // System.out.println(defaultVar); // Inaccessible
        // System.out.println(privateVar); // Inaccessible
    }
}

package org.studyeasy;

public class Parent {

public int publicVar = 1;

protected int protectedVar = 2;

int defaultVar = 3;

private int privateVar = 4;

}

package org.anotherpackage;

import org.studyeasy.Parent;

public class Child extends Parent {

public void display() {

System.out.println(publicVar); // Accessible

System.out.println(protectedVar); // Accessible

// System.out.println(defaultVar); // Inaccessible

// System.out.println(privateVar); // Inaccessible

}

Output:

1
2

Explanation:

publicVar and protectedVar are accessible in Child.
defaultVar is not accessible because Child is in a different package.
privateVar is never accessible outside Parent.

Conclusion

Access modifiers are fundamental to controlling access and ensuring data encapsulation in Java. By strategically using public, default, protected, and private modifiers, developers can safeguard their code against unauthorized access and modifications, leading to more secure and maintainable applications.

Key Takeaways:

Public: Accessible from anywhere.
Default: Accessible within the same package.
Protected: Accessible within the same package and subclasses.
Private: Accessible only within the declaring class.
Understanding access modifiers enhances code security and integrity.
Proper use of access modifiers facilitates better inheritance management.

Mastering access modifiers empowers you to design robust Java applications with clear access control and encapsulation, laying the foundation for scalable and secure software development.

Note: This article is AI generated.

S07L23 – Access modifiers in Java without inheritance

Understanding Access Modifiers in Java: A Comprehensive Guide

Table of Contents

Introduction

Table of Access Modifiers

Public Access Modifier

Overview

Syntax and Usage

Key Concepts

Example Explained

Default Access Modifier

Overview

Syntax and Usage

Key Concepts

Example Explained

Protected Access Modifier

Overview

Syntax and Usage

Key Concepts

Example Explained

Private Access Modifier

Overview

Syntax and Usage

Key Concepts

Example Explained

Access Modifiers and Inheritance

Overview

Public and Protected in Inheritance

Default and Private in Inheritance

Example Explained

Conclusion