Java Collections Framework: Which statement accurately describes java.util.ArrayList?
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AThe elements in the collection are ordered.
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BThe collection is guaranteed to be immutable.
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CThe elements in the collection are guaranteed to be unique.
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DThe elements in the collection are accessed using a unique key.
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EIt sorts elements by natural order automatically.
Answer
Correct Answer: The elements in the collection are ordered.
Explanation
Introduction / Context: ArrayList is a resizable array implementation of the List interface. Understanding its ordering, mutability, and uniqueness properties prevents misuse and bugs.
Given Data / Assumptions:
- We consider default
ArrayListbehavior.
Concept / Approach: ArrayList maintains elements in insertion order and supports indexed random access. It is mutable (add, remove, set). It does not enforce uniqueness (duplicates allowed). It is not key-based; key/value access belongs to map types. It does not automatically sort; use Collections.sort or list.sort explicitly.
Step-by-Step Solution:
Ordering: preserves insertion order → True.Mutability: supports modifications → Not immutable.Uniqueness: duplicates permitted → Not guaranteed unique.Keyed access: not applicable to lists → False.Automatic sorting: not performed by ArrayList → False.Verification / Alternative check: Javadoc for ArrayList emphasizes random access and ordering by index, not uniqueness or automatic sorting.
Why Other Options Are Wrong:
- Immutable: incorrect; ArrayList is mutable.
- Unique elements: not enforced.
- Unique key access: describes maps.
- Automatic sorting: requires explicit sort calls.
Common Pitfalls: Assuming uniqueness due to confusion with Set; assuming natural ordering without sorting; expecting thread safety (ArrayList is not synchronized by default).
Final Answer: The elements in the collection are ordered.