Sort Objects by Comparator

[nazeer hussain]

Hi Guys

Can anyone knows the code to Sort the collection of objects, having two integer data types say a,b and assume the object is POJO which will not be implemented with any interface(Serializable/Comparator/..). Requirement is as follows.

Arraylist
- POJO
- int a = 100
- int b = 150
- POJO
- int a = 75
- int b = 125
-
5 items


list Ordered by asc based a values

list Ordered by asc based b values

using Comparator
-----------------------------

Thanks
Nazeer

:roll:

[Chandra Bhatt]

Hi Nazeer,

Can you give a little code here, so that we could think of, what exactly the issue is?



Regards,
cmbhatt

[Chandra Bhatt]

package arrays;
import java.util.*;
 
public class TestSorting {
 
public static void main(String... args) {
Object[] obj = {23,6,86,2,1,64};

Arrays.sort(obj,new Comparator<Object>() {
public int compare(Object o1,Object o2) {
return ((Integer)o2).compareTo((Integer)o1);
}
});

for(Object o : obj) {
System.out.println(o);
}



}
}
 

Is this solution to your question?


Regards,
cmbhatt
[ April 16, 2007: Message edited by: Chandra Bhatt ]

[Naveen K Garg]

Also look at following thread

Sorting

Regards
Naveen

[Burkhard Hassel]

Hi ranchers,

interface Comparable is used when you have access to the class and you can implement it.

interface Comparator can be used, when you want to sort any class.

You set up a Comparator for any item you want to sort.
If you want to use generics, the name of the class to be sorted goes into the < >.

Here's an example, to compare the legs of animals.

import java.util.*;
 
class Main { // Demo
public static void main(String... args) {
Comparator<Animal> legSorter = new LegComparer();
List<Animal> zoo = new ArrayList<Animal>();
zoo.add(new Animal("Centipede", 100));
zoo.add(new Animal("Dog", 4));
zoo.add(new Animal ("Clown Fish", 0));
zoo.add(new Animal("Coccinella heptempunctata", 6));
System.out.println("unsortet");
for(Animal a:zoo)
System.out.println(a);
System.out.println();
System.out.println("sorted");
Collections.sort(zoo, legSorter); // <- comparator goes here
for(Animal a:zoo)
System.out.println(a);
}
}
 
// you have to set up your own class for a comparator:
class LegComparer implements Comparator<Animal>{
public int compare(Animal o1, Animal o2) {
return o1.legs - o2.legs;
}
}
 
// class NameComparer not ready
 
// following class shall be given:
class Animal { // implements nothing
String name;
 
int legs;
 
Animal(String name, int legs) {
this.name = name;
this.legs = legs;
}
public String toString() {
String out = "Animal ";
out += name;
out += ", ";
out += legs;
out += " legs.";
if(legs==6)
out += "\t BUG WARNING!";
return out;
}
}
 

 

Write your own comparators using that scheme (e.g. to sort the animals name or to sort your pojos).


Yours,
Bu.

[nazeer hussain]

Thank you guys for your reply. Got the solution.