Possible Duplicate:
Sorting a collection of objects
Sorting an ArrayList of Contacts based on name?
A quick question for you:
I've got an ArrayList<MyObject> filled with MyObject objects. I would like them to be sorted based on an integer variable of MyObject.
Is there a ready way to implement this or will I have to write a quicksort/mergesort myself?
Thank you for your time, Dimitris
You need to implement Comparable interface and override the compareTo. Following example I have assumed that there is a member variable 'name' on which you will be comparing the objects.
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
class MyObject implements Comparable<MyObject>{
private String name;
private int id;
public String getName() {
return name;
}
public MyObject(String name, int id) {
super();
this.name = name;
this.id = id;
}
@Override
public int compareTo(MyObject o) {
return name.compareTo(o.getName());
}
@Override
public String toString() {
return name+"\t"+id+"\n";
}
}
public class Test {
public static void main(String[] args) {
List<MyObject> list = new ArrayList<MyObject>();
list.add(new MyObject("John", 10));
list.add(new MyObject("Mark", 11));
list.add(new MyObject("Steve", 9));
Collections.sort(list);
System.out.println("Sorted list is :"+list);
}
}
You can also use the Collections.sort() libraries and pass in your collections (ArrayList) and a specifically designed Comperator for your objects.
http://docs.oracle.com/javase/7/docs/api/java/util/Collections.html[enter link description here][1]
You want to look at Comparators, they let you define the sort order whatever way you want. Here's the doc http://docs.oracle.com/javase/7/docs/api/java/util/Comparator.html
You can use Array.sort(...) You must only implement a Comparator for your MyObject or make it Comparable.
class MyObject{ private int num; /*constructor, setter and getter for num here*/ }, friend.