use
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A uses B: A calls a method (sends a message to) an object of class B or creates, receives, or returns an object of class B.
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containment
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A has a B: special case of use - an object of class A contains an object of B
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inheritance
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B is a A: specialization - B extends A (is a subclass of A) if B has all the variables and methods of A (and more).
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In the class definition of B, the child class, there is no need to repeat declarations of variables and methods of A, they are assumed to be there. The definition of B has the additional variables and methods of B.
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