Difficulty: Medium
Correct Answer: The Test1 hashCode() method is less efficient than the Test2 hashCode() method.
Explanation:
Introduction / Context:
This problem contrasts two implementations related to hashing. One class returns a constant hash code; the other attempts to compute a value-based hash but misspells the method name. The question asks which statement is true in practice.
Given Data / Assumptions:
Test1.hashCode()
correctly overrides Object.hashCode()
and always returns 42.Test2.hashcode()
(lowercase “c”) does not override Object.hashCode()
; it is just an unrelated method.
Concept / Approach:
For hash-based collections, a constant hash code leads to worst-case bucket collisions, degrading operations to linear time, which is considered less efficient behaviorally. In contrast, a value-dependent hash (if it actually overrides hashCode()
) would typically distribute instances better. Even though Test2
failed to override due to a spelling error, the intended comparison is between a constant hash and a value-derived hash: the constant-hash approach is less efficient for hashing purposes.
Step-by-Step Solution:
hashCode()
→ constant → maximal collisions → poor hashing efficiency.Test2: as written, does not override; however, a correctly spelled value-based hash (hashCode()
) is the better practice and more efficient for hashing.
Verification / Alternative check:
Insert numerous Test1
instances into a HashSet
and measure throughput versus a class with a data-distributed hash; collisions will make operations slower for the constant hash case.
Why Other Options Are Wrong:
Test1
overrides correctly.
Common Pitfalls:
Equating “compiles” with “good for performance.” Also, overlooking case sensitivity in method overriding (Java is case-sensitive).
Final Answer:
The Test1 hashCode() method is less efficient than the Test2 hashCode() method.
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