Java Classes and objects

Classes

A class is a blueprint for creating objects. Class combines data and method and work as a single unit. Class can contain fields ( variables ) and methods.

Fields are the attributes or properties of class.

Methods are describe the behavior.

Components of class:

1. Fields: These are the variables defined inside the class

2. Methods: These are independent code blocks that can complete a specific task.

3. Constructor: Constructor is a special method. Class and constructor names are the same

4. Modifiers: Modifiers are private, public, protected, etc. These are defines how can be access the class properties and methods.

A simple class syntax:

class MyClass{
    
}

Now a class syntax with the four class components:

class Person{
    public String person_name; // class fields (attributes or properties) with public modifier
    private String person_address; // class fields (attributes or properties) with private modifier


    // Constructor take the fields value by constructor parameters and set the value to class fields
    public Person(String person_name, String person_address) {
        this.person_name = person_name;
        this.person_address = person_address;
    }

    // Class method
    public void printPersonDetails(){
        System.out.println("Person name is : " + person_name + " and address is : " + person_address);
    }
}

Objects

Object is an instance of a class. It is a real world entity. Syntax of create a object is:

// Class_name object_name = new Class_name();

With the Person class example, we can create objects for a different person. Here the important thing is the Person class constructor takes 2 parameters. That's why we need to provide these values when Constructor is calling.

Now let's create a class Main which will have a main method and here let's create multiple objects of the Person class

class Main{

    public static void main(String[] args) {

        // a object of john
        Person john = new Person("John", "New York");
        // now we can access the class method and fields by john
        john.printPersonDetails(); // output : Person name is : John and address is : New York



        // another object of rahim
        Person rahim = new Person("Rahim", "Dhaka");
        // now we can access the class method and fields by rahim
        rahim.printPersonDetails(); // output : Person name is : Rahim and address is : Dhaka

    }
}

We can create multiple objects of a class and each object is different from other objects