Java Class Attributes (Fields)
In Java, variables declared inside a class are known as attributes or
fields. They represent the state (data) of an object and define its
characteristics. For example, a Person class may contain attributes like
name, age, and city.
Key point: Attributes belong to a class, and each object
created from that class gets its own copy of those attributes.
Declaring Attributes in a Class
You define attributes inside a class but outside any method.
public class Rectangle {
int width = 10;
int height = 5;
}
Here, width and height are attributes of the Rectangle class.
Accessing Attributes
To access an attribute, create an object of the class and use the dot (.)
operator.
public class Rectangle {
int width = 10;
public static void main(String[] args) {
Rectangle rect = new Rectangle();
System.out.println("Width: " +
rect.width);
}
}
Output
Width: 10
Modifying Attribute Values
Attributes can be changed after object creation.
public class Rectangle {
int width;
public static void main(String[] args) {
Rectangle rect = new Rectangle();
rect.width = 25; // modify
attribute
System.out.println(rect.width);
}
}
Output
25
Overriding Default Values
If an attribute has an initial value, you can override it for a specific
object.
public class Product {
double price = 99.99;
public static void main(String[] args) {
Product item = new Product();
item.price = 79.99; // override default
value
System.out.println(item.price);
}
}
Using final Attributes (Constants)
If you want an attribute’s value to remain constant, declare it with the
final modifier. Such attributes cannot be reassigned.
public class MathConstants {
final double PI = 3.14159;
public static void main(String[] args) {
MathConstants m = new
MathConstants();
System.out.println(m.PI);
}
}
Attempting to change PI would cause a compile-time
error.
Attributes and Multiple Objects
Each object maintains its own attribute values. Changing one object does
not affect another.
public class Counter {
int value = 5;
public static void main(String[] args) {
Counter c1 = new Counter();
Counter c2 = new Counter();
c2.value = 20; // change only
c2
System.out.println(c1.value);
System.out.println(c2.value);
}
}
Output
5
20
Classes with Multiple Attributes
Classes often contain several attributes representing a complete
entity.
public class Employee {
String firstName = "Riya";
String lastName = "Sharma";
int age = 28;
public static void main(String[] args) {
Employee emp = new Employee();
System.out.println("Name: " + emp.firstName +
" " + emp.lastName);
System.out.println("Age: " +
emp.age);
}
}
