Which of the following statements about Java Collections is correct?

Question

BlackTom AI · Accepted Answer

The question asks about the Java Collections framework and what statement is correct about them.
Option 1: 'A HashSet can only store duplicate elements.' This is incorrect because a HashSet is designed to store unique elements; it automatically rejects duplicates.
Option 2: 'A HashMap requires its keys to be primitive types.' In Java, map keys must be objects (non-primitive). While you can use wrapper classes like Integer as keys, you cannot require primitive types; primitives cannot be used as generic type parameters directly. So this statement is false.
Option 3: 'A HashMap can store key–value pairs, where both keys and values are objects (non-primitives).' This is true. HashMap stores mappings from key objects to value objects, and both keys and values are references to objects (wrapping primitives if needed).
Option 4: 'An ArrayList always has a fixed length.' This is incorrect because ArrayList is dynamic in size; it grows as elements are added.
Option 5: 'The size of an ArrayList must be fixed when it is created.' This is also false since an ArrayList can be grown or shrunk after creation by adding or removing elements.
In summary, only Option 3 accurately reflects Java Collections behavior. All other statements misstate the capabilities of HashSet, HashMap, or ArrayList.

Which of the following statements about Java Collections is correct?单项选择题

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