questions on Generic

[Mohit G Gupta]

1.can i add objects of class say A to NavigableSet,SortedSet without extending comparator interface ?
2.is the same true when objects are used as keys in NavigableMap,SortedMap ?
3.is the same true when objects are added in PriorityQueue ?



4.If i add objects of some class(say A) and Integer to a NavigableSet,SortedSet,then would by making class extend comparator interface,these two can be inserted to Set ?
5.

KB Book

Sorting with Comparator

import java.util.*;
class GenreSort implements Comparator<DVDInfo> {
public int compare(DVDInfo one, DVDInfo two) {
return one.getGenre().compareTo(two.getGenre());
}
}

Using the PriorityQueue Class

class PQ {
static class PQsort
implements Comparator<Integer> { // inverse sort
public int compare(Integer one, Integer two) {
return two - one; // unboxing
}
}

why is the PQsort class not following the same syntax as used in the GenreSort class ?

return one.getGenre().compareTo(two.getGenre());
return two - one;//WHERE IS THE CALL TO COMPARE TO

6.is there any way to view elements added to HashMap or HashSet or LinkedHashSet or LinkedHashMap in sorted order ?

[Ankit Garg]

To add any objects to any sorted collection like SortedSet or PriorityQueue, your objects must implement Comparable not Comparator. If your objects don't implement Comparable, then you can use a Comparator object to sort the collection...

[Mohit G Gupta]

thanks ankit.



but what about question 4,5,6

[Mohit G Gupta]

can anyone answer my queries

[Ankit Garg]

4. To be able to add elements to a sorted collection, the elements must be comparable to each other. If they are not, then you'll have to use a Comparator instance to sort the collection (again the elements we add to the collection need not implement Comparator, we'll use an additional Comparator instance to sort the collection).

5. In the compare method, you have to return an int value. You can use anything inside of the compare method to calculate which of the two objects is greater than the other.

6. There is no direct way to sort Maps or Sets. HashMap and HashSet are not even ordered (they don't maintain any order of elements), so you can't sort them...