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Unfortunately, it is impossible to extend an instantiable class (as opposed to an {{abstract}} class) by adding a value or field in the subclass while preserving the {{equals()}} contract. It is therefore recommended to useUse composition rather than inheritance to achieve the desired effect \[[Bloch 2008|AA. Bibliography#Bloch 08]\]. This compliant solution adopts this approach by adding a private {{card}} field to the {{XCard}} class and providing a {{public}} {{viewCard()}} method. |
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