An association represents a relationship between classes. It represents a mechanism that allows objects to communicate with each other. It describes the connection between different classes.
Association can be unidirectional or bi-directional.
A unidirectional association implies that an object of the class from which the arrow is originating, i.e., the class that has the no-arrowhead side of the association may invoke methods on the class towards which the arrow is pointing.
A bi-directional association means that either object in the association may invoke methods on the other.
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