Chapter 17: Problem 9

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

Short Answer

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" character, also known as a type wildcard, in the context of generic programming? Answer: The "?" character, or type wildcard, represents an unknown or unspecified type in generic programming. It allows you to create more versatile and reusable code by enabling methods, interfaces, or classes to work with multiple types simultaneously without specifying a particular type during instantiation.

Step by step solution

Definition of ? Character

The "?" character, also known as a type wildcard, is used in generic type notation to represent an unknown or unspecified type. It provides a way to create more flexible and reusable code by allowing you to work with multiple types simultaneously and making your methods, interfaces, or classes more versatile.

Wildcards in Generic Programming

In the context of generic programming, wildcards allow you to create generic methods and classes that work with multiple types, without specifying a particular type during instantiation. For example, you can have a method that accepts a List of any type or a class that can be parameterized by more than one type.

Upper Bounded Wildcards

You might also encounter upper bounded wildcards, which are denoted by syntax like `? extends Type`. This means that the wildcard represents a type that is a subclass of (or equal to) the specified type. This can be useful when you want your method or class to work with types that are related through inheritance. Example: ```java public static void printNumbers(List numbers) { for (Number num : numbers) { System.out.println(num); } } ```

Lower Bounded Wildcards

Similarly, you might come across lower bounded wildcards, represented by `? super Type`. This syntax indicates that the wildcard represents a type that is a superclass of (or equal to) the specified type. This gives you more flexibility when working with types that share a common ancestry. Example: ```java public static void addObject(List numbers, Integer numberToAdd) { numbers.add(numberToAdd); } ``` In conclusion, the "?" character or type wildcard is an essential part of generic programming in languages like Java, offering increased flexibility and adaptability for handling different types in a consistent and reusable manner.

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

Short Answer

Step by step solution

Definition of ? Character

Wildcards in Generic Programming

Upper Bounded Wildcards

Lower Bounded Wildcards

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