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Hi all,
Which of these statements concerning Map are true ?
a. It is permisible for a map to contain itself as a key.
b. values() method return an instance of Set.
c. The Map interface extends the collection interface.
d. All keys in a map are unique.
e. All map implementations keep the keys sorted.
I know that "c" is false.
a. false. It is permisible for a map to contain itself as a value & not as a map
But I am confused about the other options.
the values() method in Map returns a Collection, so does that make "b" true???
And does All map implementations keep the keys sorted.???
Thx in advance
Aruna
 
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Hi! Aurna
First I would like to address point b. of your question.
The option b is not true. I looked up the tutorial on maps in java.sun.docs and I quote :
" values(): The Collection of values contained in the Map. This Collection is not a Set, as multiple keys can map to the same value. "
Second - point d.
All keys in a map are unique - true. Again from java.sun.docs.
"A map cannot contain duplicate keys: Each key can map to at most one value. "
Third - point e.
All map implementations keep the keys sorted - false
Only sorted maps keep the keys sorted. Example of such a map is a TreeMap.
An example of an unsorted map is the HashMap.
I am not sure about the point a.
Hope this helps.
Latha

Originally posted by Aru Ven:
Hi all,
Which of these statements concerning Map are true ?
a. It is permisible for a map to contain itself as a key.
b. values() method return an instance of Set.
c. The Map interface extends the collection interface.
d. All keys in a map are unique.
e. All map implementations keep the keys sorted.
I know that "c" is false.
a. false. It is permisible for a map to contain itself as a value & not as a map
But I am confused about the other options.
the values() method in Map returns a Collection, so does that make "b" true???
And does All map implementations keep the keys sorted.???
Thx in advance
Aruna


 
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52
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a. is false. A map cannot contain itself as a key (it can contain itself a s a value though).
Such questions are best answered by looking into the API docs. Even tutorials cannot provide complete factual points about the classes. They only give a general idea.
HTH,
Paul.
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