Java Classes and Objects - Advanced Concepts

Classes: Components and Features

Fields / Instance Variables: Object ke state ko represent karte hain.
Methods: Behavior ya functionalities jo objects perform karte hain.
Constructors: Special methods, jo object creation par initialize karte hain.
Static Members: Class level fields aur methods, jo objects ki bajay class associated hote hain.
Access Modifiers: public, private, protected modifiers se access control hota hai.
Encapsulation: Data ko hide karke methods ke through access dena best practice hai.

Advanced Object Creation and Usage

public class Car {
    private String model;
    private int year;
    
    // Constructor
    public Car(String model, int year) {
        this.model = model;
        this.year = year;
    }
    
    // Getter and Setter (Encapsulation)
    public String getModel() {
        return model;
    }

    public void setModel(String model) {
        this.model = model;
    }
    
    public int getYear() {
        return year;
    }

    public void setYear(int year) {
        this.year = year;
    }
    
    // Behavior method
    public void display() {
        System.out.println("Model: " + model + ", Year: " + year);
    }
}

public class Main {
    public static void main(String[] args) {
        Car car1 = new Car("Toyota", 2020);
        car1.display();
        
        car1.setYear(2021);
        System.out.println("Updated year: " + car1.getYear());
    }
}

Multiple Objects and References

Ek class se kayi objects banaye ja sakte hain, alag alag references se. Har object apna unique state rakhta hai.

Car carA = new Car("Honda", 2018);
Car carB = new Car("Ford", 2019);

carA.display();  // Honda 2018
carB.display();  // Ford 2019

The `this` Keyword

this current object ko refer karta hai. Ye ambiguity door karta hai jab instance variable aur local variables ka naam same hota hai.

public void setModel(String model) {
    this.model = model;  // 'this.model' instance variable, 'model' parameter
}

Constructor Overloading

Ek class me multiple constructors banaye ja sakte hain alag alag parameters ke saath, jise constructor overloading kehte hain.

public class Car {
    private String model;
    private int year;

    public Car() {
        this.model = "Unknown";
        this.year = 0;
    }

    public Car(String model) {
        this.model = model;
        this.year = 0;
    }

    public Car(String model, int year) {
        this.model = model;
        this.year = year;
    }
}

Summary