In any application Classes are not directly used. But instance / Object of the classes are used for executing the business logic. Representing the relation between these objects at any point of time is called Object diagram.
With the help of an object diagram we can understand how the classes are interact at run time.
Object diagram concentrates on some particular objects and attributes and the links between the objects and it tells how a system evolves over time. Object diagram is used to show a particular model of system which we are interested
Elements of an Object diagram
As object diagram is the instance of classes, it consists of same element as the class diagram.
Example: Let us consider the example of Course and Students class. The class diagram for this can be as below.
Here we can notice that a course has many Students, We can represent the same at the run time using an Object diagram as below.