Object composition refers to the logical or conceptual structure of the information , not the implementation or physical data structure used to represent it. For example, a sequence differs from a set because (among other things) the order of the composed items matters for the former but not the latter.
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In OOP, IS-A relationship is completely inheritance . This means, that the child class is a type of parent class. For example, an apple is a fruit. So you will extend fruit to get apple.
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