What is a Class?

About

A class in Java is a blueprint or template for creating objects. It defines the state (fields/attributes) and behavior (methods) that objects of that class will have.

Characteristics of a Class

1. Defines State (Attributes)

• Represented by fields/variables inside the class.

• Example: String name;, int age;.

2. Defines Behavior (Methods)

• Defined by functions inside the class.

• Example: void eat() {}, void sleep() {}.

3. Can Contain a Constructor

• Special method used to initialize an object.

• Example: Person(String name, int age) { this.name = name; this.age = age; }.

4. Objects are Created from a Class

• A class itself is just a definition; actual objects are instantiated from it.

Example of a Class in Java

// Class Definition (Blueprint)
class Person {
    // Attributes (State)
    String name;
    int age;

    // Constructor (Used to initialize object)
    Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    // Methods (Behavior)
    void introduce() {
        System.out.println("Hi, I am " + name + " and I am " + age + " years old.");
    }
}

// Main Class
public class Main {
    public static void main(String[] args) {
        // Creating Objects from Class
        Person person1 = new Person("Alice", 25);
        Person person2 = new Person("Bob", 30);

        // Calling Methods
        person1.introduce(); // Hi, I am Alice and I am 25 years old.
        person2.introduce(); // Hi, I am Bob and I am 30 years old.
    }
}

How Classes Work in Memory

• The class definition itself is stored in method area (Metaspace in Java 8+).

• When an object is created, memory is allocated in the heap, and the reference variable (like person1) is stored in the stack.