Class

✅ Why do we need class?

• collect each student’s charecteristics in one class
• create one student class

• and save one student’s name, age, grade in one class

• there is int type, String type in Java
• we save numbers in int type and letters, words in String type
• why not create Student type when we need, and save students in Student type class?

👎🏻 before

• student1, student2 contents are distributed into arrays
• more difficult to know about student1

String[] studentNames = {"학생1, 학생2"}
int[] studentAges = {15, 16};
int[] studentGrades = {90, 80};

👍🏻 after

• create student class

public class Student {

    String name;
    int age;
    int grage;
}

• create student in Main class
• save one student fields in one class

public class studentMain {
    public static void main(String[] args) {
        Student student1 = new Student(); //create student
        student1.name = "student1"; //save student fields
        student1.age = 15;
        student1.grage = 90;
    }
}

✔️ class is like a blueprint

• create types that developer needs
• create student blueprint
• and save student1, student2…

✅ Class, Object, Instance

• student class : class
• student1, student2… : instance
• student1 and student2 are different objects

• student1 object is an instance of student class

• class is a blueprint of an instance
• defines field and method of instance
• instance is created based on class
• object and instance are used interchangeably