Java Tutorial - 27 Class & Objects in Java - StudyViral

Java Tutorial - 27 Class & Objects in Java - StudyViral

 Class
A class is a user defined prototype or blueprint from which objects are created.
We can also say class is collection of data members and member functions/methods.
where data members are variable and member functions/methods are used to access
data members.
Keyword: class

Note: Every Single Java file can have only single/one public class.
We can't have two or more class as public within single java file.

Object
Objects are instance of class. In other words object reference are memory locations
where object data is saved.
Object of predefined or user defined classes can be created by using new operator.

Constructor
Constructors are special method which has same name as that of class name.

 class Student{
    String name;//data members
    int rollno;

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getRollno() {
        return rollno;
    }
    public void setRollno(int rollno) {
        this.rollno = rollno;
    }
    //2 Member Functions
    public void sleep() {
        System.out.println(name+" "+rollno + " is Sleeping" );
    }
    public void study() {
        System.out.println(name+" "+rollno + " is Studing" );
    }
}

public class DemoClassObject {

    public static void main(String[] args) {
        Student s1;//s1 is object of Student Class
        s1 = new Student();//Initialize
              
        s1.setName("Hardeep");
        s1.setRollno(101);
        System.out.println("Name :: "+s1.getName());
        System.out.println("Rollno :: "+s1.getRollno());
        s1.sleep();
        s1.study();
    }
}