Careeroza

Creating a Class and Objects

Your First Class

Example

Create objects with the new keyword. Use the dot . to access fields.

public class Main {
    public static void main(String[] args) {
        Student s1 = new Student();
        s1.name = "Kavya";
        s1.rollNo = 101;
        s1.cgpa = 8.7;

        Student s2 = new Student();
        s2.name = "Rohit";
        s2.rollNo = 102;

        System.out.println(s1.name + " " + s1.rollNo + " " + s1.cgpa);
        System.out.println(s2.name + " " + s2.rollNo + " " + s2.cgpa);   // cgpa not set -> 0.0
    }
}

class Student {
    String name;
    int rollNo;
    double cgpa;
}

Output

Kavya 101 8.7
Rohit 102 0.0

Key Points

Each object has its own copy of the fields. Changing s1.name does not change s2.name.
Fields get default values: 0, 0.0, false, null.
A variable like s1 holds a reference to the object, not the object itself.
In real projects each public class lives in its own file (Student.java). In these examples extra classes sit in the same file without public.