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Chapter 17: Problem 12

In generic type notation, does the extends key word establish an upper boundary or a lower boundary?

Short Answer

Expert verified
Answer: In generic type notation, the "extends" keyword establishes an upper boundary for a type parameter.

Step by step solution

01

Understanding Generic Type Notation

Generics in programming languages enable us to define a single generic type that can work with multiple types while providing type-safety. The type parameter is usually represented within angle brackets (e.g., ), where T is the type variable that will be replaced by an actual type during runtime.
02

Understanding the Extends Keyword

The "extends" keyword is used in generic type bounds to define a condition for the type variable (T). That means you can restrict the type variable to inherit from a specific class (upper bound) or be a superclass of a specific class (lower bound).
03

Determine if Extends Establishes an Upper or Lower Boundary

When using the "extends" keyword in generic type notation, it establishes an upper boundary for the type parameter. This means that the type parameter T must either be of the specified type or be a subclass (inherit from) of that type. For example, if we have a generic type notation like \, this means that T can be any type that is a subclass of Number or Number itself. This establishes an upper boundary, as T can be any class that is "up to the level" of the specified class (Number) in the inheritance hierarchy.

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Most popular questions from this chapter

Why is it risky to store objects of different types in an ArrayList?

During the process of erasure, when the compiler encounters a generic class, interface, or method with an unbound type parameter, such as or , what does it replace the type parameter with?

In generic type notation, what does the \(?\) character (the type wildcard) indicate?

In generic type notation, does the super key word establish an upper boundary or a lower boundary?

Assume we have used the statement shown in Checkpoint 17.3 to instantiate the ArrayList class. If we attempt to store an object that is not of the allowable type in the ArrayList, will we see an error message at compile time or at runtime?
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