Using the Comparator Interface.Please Help.

Question

Hello there,
I am trying out this example regarding the Comparator Interface.
It works fine, but I havent really understood this at all.
It deals with reverse sorting.
import java.util.*;
class MyComp implements Comparator {
public int compareTo(Object a,Object b)
String aStr,bStr;
aStr = (String)a;
bStr = (String)b;
return bStr.compareTo(aStr)
class MyComparator {
public static void main(String[] args) {
// Create a Tree Set
TreeSet ts = new TreeSet(new MyComp());
ts.add("C");
ts.add("A");
ts.add("P");
ts.add("Z");
ts.add("B");
System.out.println(ts)
Output : [Z, P, C, B, A]
I have not understood the following at all:
1) We are implementing the Comparator Interface in class MyComp.
Now where is this being called in the MyComparator class?
2) How is the reverse sorting taking place.?
How is this comparing the different instances of the MyComparator class
when I havent even instantiated the MyComparator class ?
3) How is the interface method compare To(Object a,Object b) being invoked?
Please can some please answer my questions.
Regards

Answer 1

class MyComp implements Comparator {
public int compareTo(Object a,Object b)
String aStr,bStr;
aStr = (String)a;
bStr = (String)b;Your reverse ordering is happening here.
If you were to write
return aStr.compareTo(bStr)
the ordering would be in normal order.
>
return bStr.compareTo(aStr)The comparator that the treeSet uses is declared and instantiated here
TreeSet ts = new TreeSet(new MyComp());
1) We are implementing the Comparator Interface in
class MyComp.
Now where is this being called in the MyComparator
or class? The comparator is being used by the TreeSet to order your entries
>
>
2) How is the reverse sorting taking place.?Explained above. For further explaination look up comparator and String.compareTo()
How is this comparing the different instances of
of the MyComparator class
when I havent even instantiated the MyComparator
or class ?Also explained above
3) How is the interface method compare To(Object
a,Object b) being invoked?Internally by the TreeSet
I hope this helped a little