Object and Class

OOPS (Object-Oriented Programming System) is a programming paradigm that solves problems by organizing code around objects, which represent real-world entities. It uses real-world concepts to model problems and solutions.

Main OOP Concepts:

• Inheritance
• Polymorphism
• Encapsulation
• Abstraction

Class : 

A class is declared using the class keyword. It acts as a blueprint that defines the structure and behavior (data and methods) of objects. 

A class can contain:

• Fields (variables)
• Methods
• Constructors
• Blocks (static or instance)
• Nested classes and interfaces

Syntax:

class ClassName {  
    // fields  
    // methods  
}                                

Object :

An object is an instance of a class that represents a real-world entity. It has three main characteristics:

• State → represents data or properties of the object.
• Behavior → represents functionality (methods) of the object.
• Identity → represents a unique reference to the object in memory.

Ways to Create/Initialize an Object in Java :

1. Using new keyword

MyClass obj = new MyClass();   

2.Using Reflection (Class.forName(), getDeclaredConstructor().newInstance())

MyClass obj = (MyClass) Class.forName("MyClass").getDeclaredConstructor().newInstance();  

3.Using clone() method

MyClass obj2 = (MyClass) obj1.clone();   

4. Using Deserialization

(Object is recreated from a saved state).

For more details click 👉here 

A class is initialized in Java when:

1. An instance of the class is created using the new operator.
2. A static method of the class is invoked.
3. A static field of the class is accessed or assigned (unless it’s a compile-time constant).
4. Reflection is used (e.g., Class.forName("MyClass")).

Example :

class MyClass {
    static {
        System.out.println("Class is being initialized!");
    }

    MyClass() {
        System.out.println("Constructor called: Object created");
    }

    static void staticMethod() {
        System.out.println("Static method called");
    }
}

public class TestInitialization {
    public static void main(String[] args) throws Exception {
        // Class initialization by creating object
        MyClass obj1 = new MyClass();

        // Class initialization by calling static method
        MyClass.staticMethod();

        // Class initialization using reflection
        MyClass obj2 = (MyClass) Class.forName("MyClass").getDeclaredConstructor().newInstance();
    }
} 

Output:

Class is being initialized! Constructor called: Object created Static method called Constructor called: Object created

Explanation:

• The static block executes once when the class is initialized.
• Class is initialized when an object is created, a static method is called, or using reflection.
• Each new object triggers the constructor but does not re-run the static block.