Question at position 5 What does this code accomplish? ArrayList l = new ArrayList(); l.add( ... some data ); repeat many times ... ArrayList m = new ArrayList( new HashSet(l));Copies l into m in sorted orderCopies l into m with no duplicates, because Set doesn't allow duplicatesCopies l into m with no changesCreates the union of l and m

Question

Question at position 5 What does this code accomplish? ArrayList<Student> l = new ArrayList<>(); l.add( ... some data ); repeat many times ... ArrayList<Student> m = new ArrayList<>( new HashSet<>(l));Copies l into m in sorted orderCopies l into m with no duplicates, because Set doesn't allow duplicatesCopies l into m with no changesCreates the union of l and m单项选择题

A

Copies l into m in sorted order

B

Copies l into m with no duplicates, because Set doesn't allow duplicates

C

Copies l into m with no changes

D

Creates the union of l and m

BlackTom AI · Accepted Answer

The question presents code that starts with an ArrayList l populated with data, and then creates a second ArrayList m by passing a HashSet constructed from l into the ArrayList constructor. This pattern is used to remove duplicates from the list by leveraging the Set's property of not allowing duplicate elements before converting back to a list. Option 1: 'Copies l into m in sorted order' - This is incorrect. A HashSet does not maintain a natural or insertion-based sort; it is an unordered collection. When you wrap l in a HashSet, you lose any defined ordering, and there is no subsequent sorting step, so the resulting m will not be guaranteed to be in sorted order. Option 2: 'Copies l into m with no duplicates, because Set doesn't allow duplicates' - This is the core correct idea. The process is: take l, place its elements into a HashSet (which discards duplicates), then create a new ArrayList from that Set. The resulting m contains each distinct Student exactly once, assuming proper equals and hashCode implementations in Student. The lack of duplicates is due to the Set’s property, not due to any direct sorting or identity preservation. Option 3: 'Copies l into m with no changes' - This is false. Since a HashSet is used, duplicates present in l will be removed when inserted into the Set. Moreover, since a Set is unordered, the order of elements in m will generally differ from the original order in l, so it is not a simple copy with no changes. Option 4: 'Creates the union of l and m' - This is incorrect. A union would combine the elements of two sets or lists, but here m is created solely from the Set view of l. There is no operation that combines l and m or introduces elements outside of those originally present in l. The code does not explicitly merge two collections; it simply deduplicates l and stores the result in m.

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