Map

[wei liu]

2. Which of the following allows duplicates, and introduces positional indexing.?
[a] Set
[b] Map
[c] Iterator
[d] List
Answer 2
[b] Map
I think the ans is wrong, because May cnt contain duplicates. however, which is right ans?

[Jim Hall]

Sounds like a List to me.
From API:
An ordered collection (also known as a sequence). The user of this interface has precise control over where in the list each element is inserted. The user can access elements by their integer index (position in the list), and search for elements in the list.
Unlike sets, lists typically allow duplicate elements.

[This message has been edited by Jim Hall (edited December 15, 2001).]

[Fei Ng]

answer is B)Map.
no duplicates of the Keys only. You can have duplicates values.
but not sure whats the meaning of positional indexing.

[Jim Hall]

Can't be a Map. There is no concept of positional indexing in a Map. The Map only provides a get(Object key) method for accessing its elements.

[Jeff Taylor]

I would choose answer d, because Lists allow duplicate entries and maintain their elements in a specified order. All elements in a List get an unique index, which can be used to access them ( http://java.sun.com/j2se/1.4/docs/api/java/util/List.html#get(int) ). I think that's what 'positional indexing' refers to.
/JT