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Reading Type From Unbounded Wildcard Unbounded wildcard<?> is really just a wildcard with a bound of type Object <? extends Object>. Obviously, even an unbounded wildcard instantiation holds objects that can be assigned to Object, so it’s OK to read an unbounded wildcard as the Object type : Our instantiation g1 returns type is Object. … Read more…

Object The Object class is a superclass of all other classes. This means all other classes are subclass of the Object class. Object has eleven methods : A reference variable of a superclass can be assigned a reference to any subclass derived from that superclass. Thus, a reference variable of type Object can store a reference … Read more…

Reading Type From UpperBound We have to take the two cases separately. Drawing on the analogy of a container, we’ll call getting a return value from a method on an object as a specific type reading the object as a type. Conversely, we’ll call passing arguments of a specific type to methods of the object … Read more…

Bounded Wildcards A bounded wildcard is a wildcard that uses the extends keyword just as a type variable would to limit the range of assignable types. For example : Our ‘abc’ variable is limited to holding instantiations of Gen on parameter types of A and its subclasses(B and C). So, we can assign it a Gen<A> or … Read more…

Bounded Types In some situations you define a generic type where you want to constrain the type arguments that are supplied to define a class instance so that they extend a particular class, or implement specific interfaces, or even both. The reason for this is that your generic type has to make some assumptions about … Read more…