Object composition is a way to combine objects or data types into more complex ones. Common kinds of compositions are objects used in object-oriented programming, tagged unions, sets, sequences, and various graph structures. Object compositions relate to, but are not the same as, data structures.
One of the advantages of object composition over inheritance is that it tends to promote greater code reuse. By using object composition, you gain access to other classes and methods that would be difficult to obtain via Java’s single‐inheritance model.