M&C 2: Difficulty distinguishing between the class and an object

Mastering the difference between a class and an object can be challenging for students. One experienced high school teacher recommends giving students a simple example they can relate to and remember when doubt arises. For example, tell your students: “Students in a school represent a class; you are an object.” Or, when you make cookies, we have a class called Cookie Cutter and the objects are the cookies.

The formal definition of “A class is a user-defined prototype defining a set of attributes that characterize any object of the class. An object is a unique instance of a data structure that’s defined by its class” may clarify things for some students, but examples are often more effective and helpful. Here are more examples to help understand the difference:

  • A class is like a blueprint for a house and a specific house is an object of the blueprint.
  • The concept Student is a class, and a specific student is an object of the class Student. For example, John and Bill are both objects which are instances of the class Students. Their attributes could show that both are students at Harrison High School. but the value of attributes name, address, GPA, and  date of birth will be different.
  • An object stove and an object computer are both instances of the class Appliance, but the values of their attributes are different. Both stove and computer have the attribute Price; the price of a stove is 1400 and the price of a computer is 600.
  • In the class Horse, silver and trigger are objects which are instances of the class Horse. They both have the attribute color, but the values of attribute color are different: silver is white and trigger is palomino.