Java Class Attributes

Welcome to The Coding College! In this article, we’ll explore class attributes in Java, a fundamental concept that allows you to define the properties or characteristics of a class. Understanding attributes is crucial for designing classes effectively in object-oriented programming.

What Are Class Attributes?

Class attributes (also known as fields or variables) are variables declared within a class. These attributes represent the state or properties of the objects created from the class.

Key Points:

• Attributes can be of any data type (primitive or non-primitive).
• They are defined outside methods, constructors, or blocks.
• They can have different access modifiers (public, private, protected).

Syntax

Here’s how to define attributes in a class:

class ClassName {
    // Attribute declaration
    dataType attributeName;
}

Example: Defining and Using Class Attributes

// Defining a class with attributes
class Car {
    // Attributes
    String brand;
    String model;
    int year;

    // Method to display car details
    void displayDetails() {
        System.out.println("Car: " + brand + " " + model + " (" + year + ")");
    }
}

public class Main {
    public static void main(String[] args) {
        // Creating an object of the Car class
        Car myCar = new Car();

        // Assigning values to attributes
        myCar.brand = "Toyota";
        myCar.model = "Corolla";
        myCar.year = 2020;

        // Displaying attribute values
        myCar.displayDetails();
    }
}

Output:

Car: Toyota Corolla (2020)

Access Modifiers for Attributes

Access modifiers define the visibility of attributes:

Example: Using private Attributes

To restrict access to an attribute, declare it as private and use getter and setter methods to access and modify it.

class Person {
    // Private attribute
    private String name;

    // Getter method
    public String getName() {
        return name;
    }

    // Setter method
    public void setName(String name) {
        this.name = name;
    }
}

public class Main {
    public static void main(String[] args) {
        Person person = new Person();

        // Using setter to assign value
        person.setName("Alice");

        // Using getter to retrieve value
        System.out.println("Name: " + person.getName());
    }
}

Output:

Name: Alice

Default Values of Attributes

If you don’t initialize an attribute, it will have a default value based on its data type:

Static Attributes

Attributes declared as static belong to the class rather than to any specific object.

Example:

class Company {
    // Static attribute
    static String companyName = "TechCorp";

    // Non-static attribute
    String employeeName;
}

public class Main {
    public static void main(String[] args) {
        // Accessing static attribute without creating an object
        System.out.println("Company: " + Company.companyName);
    }
}

Output:

Company: TechCorp

Final Attributes

Attributes declared with the final keyword cannot be changed after they are initialized.

Example:

class Constants {
    final double PI = 3.14159;

    void displayPI() {
        System.out.println("Value of PI: " + PI);
    }
}

public class Main {
    public static void main(String[] args) {
        Constants c = new Constants();
        c.displayPI();
    }
}

Output:

Value of PI: 3.14159

Best Practices

1. Use meaningful names for attributes to improve code readability.
2. Keep attributes private and use getter/setter methods for controlled access.
3. Use final for constants to prevent accidental modification.
4. Prefer static attributes for values shared across all instances of a class.

Practice Problems

1. Create a Book class with attributes for title, author, and price. Add methods to display the details of a book.
2. Design a Student class with attributes for name, roll number, and marks. Add getter and setter methods for controlled access.
3. Implement a BankAccount class with attributes for account number, balance, and account holder name. Add a static attribute for the bank name.

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