Mastering Java: The Ultimate Quiz for 'Thinking in Java'

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In generics, what does the '?' symbol represent?

  1. Any class that extends Number

  2. A specific type that must be defined

  3. An unknown type, also known as a wildcard

  4. A Boolean value indicating the presence of a type

The correct answer is: An unknown type, also known as a wildcard

The '?' symbol in generics represents an unknown type, also known as a wildcard. This allows for greater flexibility in defining type parameters and allows methods to be used more generally. Option A is incorrect because it is a limited definition and only includes classes that extend Number. Option B is incorrect because it contradicts the purpose of utilizing a wildcard in generics. Option D is incorrect because it does not accurately describe the purpose of the '?' symbol in generics.

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