who can explain this code?????????

[JAD]

can you Explain the workings of this code Specifically, the lines in bold font
can you?



import java.util.*;
public class WhichComparator implements Comparator {
protected Comparator base;

public WhichComparator(Comparator baseCompare) {
base = baseCompare;
}
public int compare(Object obj1, Object obj2) {
return -base.compare(obj1, obj2);
}

public static void main(String[] args) {
Vector arr = new Vector();
Random ran = new Random();

for(int i = 0; i < 10; i++)
arr.add(new Integer(ran.nextInt(100)));
System.out.println("Array before sorting!!!");
System.out.println(arr);

Comparator c = new RevComparator(new IntegerComparator());

Collections.sort(arr, c);

System.out.println("Array after sorting!!!");
System.out.println(arr);
}
} // End of class WhichComparator

class IntegerComparator implements Comparator {
public int compare(Object o1, Object o2) {
Integer i1 = (Integer) o1;
Integer i2 = (Integer) o2;
if(i1.intValue() == i2.intValue())
return 0;
else if(i1.intValue() > i2.intValue())
return 1;
else
return -1;
}
} // End of class IntegerComparator

[JGRobinson]

Hi,

Here goes,

the Collections.sort method as it does not know what items you are attempting to sort it requires a Comparator class to help.

A Comparator class has a two methods, compare and equals - I believe that sort only uses the compare method.

The compare method is used to compare the two arguments.

If they are equal - return 0
if the first is greater than the second - return 1
if the second is greater than the first - return -1

The line

public int compare(Object obj1, Object obj2) {
return -base.compare(obj1, obj2);
}

Looks to be taking the return from the base.compare method, and negativising it, thus creating a reverse sort.

The other two lines highlighted

Comparator c = new RevComparator(new IntegerComparator());

Collections.sort(arr, c);

are just creating a Comparator object , and using the static sort method of Collections to perform the sort.

Hope this helps
Graham