Java Classes and Objects

Java is an object-oriented programming language, so classes and objects are the foundation of Java programs.

1. What is a Class?

A class is a blueprint or template that defines the attributes (variables) and behaviors (methods) of objects.

Class name starts with an uppercase letter by convention.
Attributes → Store object data.
Methods → Define actions the object can perform.

2. What is an Object?

An object is an instance of a class. It has its own copy of the class attributes and can use class methods.

public class Main {
public static void main(String[] args) {
Car car1 = new Car(); // Creating object car1
car1.brand = "Toyota"; // Setting attributes
car1.year = 2022;
car1.displayInfo(); // Calling methodCar car2 = new Car();
car2.brand = "Honda";
car2.year = 2023;
car2.displayInfo();
}
}

public class Main {

public static void main(String[] args) {

Car car1 = new Car(); // Creating object car1

car1.brand = "Toyota"; // Setting attributes

car1.year = 2022;

car1.displayInfo(); // Calling methodCar car2 = new Car();

car2.brand = "Honda";

car2.year = 2023;

car2.displayInfo();

}

📌 Output:

3. Object Syntax

new keyword creates a new object in memory.
Each object has its own copy of instance variables.

4. Multiple Objects Example

class Student {
String name;
int age;void display() {
System.out.println("Name: " + name + ", Age: " + age);
}
}

public class Main {
public static void main(String[] args) {
Student s1 = new Student();
s1.name = "Alice";
s1.age = 20;

Student s2 = new Student();
s2.name = "Bob";
s2.age = 22;

s1.display();
s2.display();
}
}

class Student {

String name;

int age;void display() {

System.out.println("Name: " + name + ", Age: " + age);

}

public class Main {

public static void main(String[] args) {

Student s1 = new Student();

s1.name = "Alice";

s1.age = 20;

Student s2 = new Student();

s2.name = "Bob";

s2.age = 22;

s1.display();

s2.display();

}

📌 Output:

5. Key Points

Class → Blueprint (defines properties and behaviors).
Object → Instance of a class (has its own state).
Attributes → Variables inside a class.
Methods → Functions inside a class.
new keyword → Creates object in memory.
Objects can have different values for the same attributes.

Java Classes and Objects