Post

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

👍🏻 after

  • create student class
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public class Student {

    String name;
    int age;
    int grage;
}
  • create student in Main class
  • save one student fields in one class
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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
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