Considering these two classes, which statement is true?\n\nclass Test1 \n{\n public int value;\n public int hashCode() { return 42; }\n}\nclass Test2 \n{\n public int value;\n public int hashcode() { return (int)(value ^ 5); }\n}

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.
  • Both classes compile.


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:

Test1: 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:

  • Compilation: both classes compile; spelling the method differently merely defines a new method.
  • “More efficient”: constant hash codes are considered worst practice for hash tables.
  • “Both override”: only 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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