Given: class Vehicle implements Comparable<Vehicle>{ int vno; String name; public Vehicle (int vno, String name) { this.vno = vno; this.name = name; } public String toString () { return vno + ":" +…

Question

Options

• A[10123:Ford, 10124:BMW]
• B[10124:BMW, 10123:Ford]
• CA compilation error occurs.
• DA ClassCastException is thrown at run time.

• A
  4% (1)
• B
  82% (23)
• C
  11% (3)
• D
  4% (1)

Explanation

TreeSet maintains elements in sorted order using the compareTo method, not insertion order. Since compareTo sorts by name alphabetically, "BMW" < "Ford" lexicographically, so BMW appears first - producing [10124:BMW, 10123:Ford].

Why the distractors are wrong:

• A is wrong because TreeSet never preserves insertion order; that's LinkedHashSet's job.
• C is wrong because Vehicle correctly implements Comparable<Vehicle>, so the compiler is satisfied.
• D is wrong because ClassCastException would occur only if the class did not implement Comparable (or Comparator wasn't provided) - here, it does.

Memory tip: Think "Tree = sorted, Hash = unordered, LinkedHash = insertion order." Whenever you see TreeSet or TreeMap, ask yourself "what does compareTo return?" - that determines the sort key, not the field order or insertion sequence.

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