![]() Thus they can be used in method input types and return types (class - remember that a class definition is really a type definition) in the ![]() Superclass of B because one cannot guarantee that code that uses M圜lass is always safe for useĪ parameterized class is a type just like any other type So, in general, M圜lass is NOT a superclass of Incompatibility problem by assigning the data value of a box of Method call is perfectly legal, from a compiler standpoint:īox instance were allowed, then we would get type In this scenario, if we have declared the variableī of type Box as above, then the following This may seem counter-intuitive, but consider theįollowing situation: Suppose the box had a settor method: The following assignment would generate a type error: Subclass of Box but that is NOT true! For instance, Relationships for specific parameterized types where the type parameter isĮxplicitly specified, as above, still work as normal. That is, Box sb = new SpecialBox("Yahoo!") It should be noted that the second definition above Consider theįollowing example, where we are trying to model a "box" that hold objects: public class OldBox ![]() So far, we've used abstract classes and polymorphismĮxtensively to model a high level of abstraction in our software systems.īut we can run into problems with type safety in doing this. When an actual concrete object is instantiated from generic code, a particular value for the generic type parameter(s) must be supplied. Generic type parameters are set to specific concrete types at construction time. Multiple generic type parameters represent separate, independent type consistencies. That is, when entities are specified by the same generic type parameter, they must all be of the same type. Generic type parameters enforce consistent type requirements across the affected code. Generic type parameters do not specify a particular entity type but rather, are placeholders for any type, perhaps within some boundaries. Some important things to remember about generics: This is opposed to the regular or "ad hoc" polymorphism that expresses abstractions in terms of inheritance hierarchies of entity types (classes) where superclasses are invariant with respect to their subclasses. Generics or "parametric polymorphism" is a technique for expressing abstraction where the code is invariant with respect to the specific type of certain entities. Written by ex-Rice graduate student Anupam Chanda for Comp212: Please also refer to the supplemental PowerPoint slides for this material, ![]() COMP 310 Java Resources Eclipse Resources ![]()
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