2

I use a linkedlist in my java program, and the element is a custom type which has three fields, one of them is of Integer type. My problem is: how to sort the linkedlist according the value of the Integer filed?

David
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  • possible duplicate of [Sort ArrayList of custom Objects by property](http://stackoverflow.com/questions/2784514/sort-arraylist-of-custom-objects-by-property) – krlmlr May 31 '13 at 17:54

4 Answers4

9

You can use the Collections.sort method with a custom Comparator. 

Collections.sort(your_list, new Comparator<YoureValueType>(){
   @Override
   public int compare(YoureValueType o1, YoureValueType o2){
        if(o1.getMagicInt() < o2.getMagicInt()){
           return -1; 
        }
        if(o1.getMagicInt() > o2.getMagicInt()){
           return 1; 
        }
        return 0;
   }
});

Edit: I just saw Alexandr comment about very large and small values on waldheinz answer. I updated my code to reflect his argument.

tfk
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3

You can use a Comparator which knows how to sort your Objects like this:

public class Foo {

    public String ignoreMe;
    public int sortOnMe;
    public Object ignoreMeToo;

    public static void main() {
        final List<Foo> unsorted = new LinkedList<Foo>();

        // add elements...

        Collections.sort(unsorted, new Comparator<Foo>() {

            @Override
            public int compare(Foo o1, Foo o2) {
                return o1.sortOnMe < o2.sortOnMe ? -1 : o1.sortOnMe == o2.sortOnMe ? 0 : 1;
            }
        });

    }

}
Waldheinz
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    this code may give the wrong answer when there is overflow. For instance, when comparing a large negative value to a large positive value, the difference may be more than the largest value that can be stored in an integer, Integer.MAX_VALUE. – Alexandr Jun 16 '11 at 09:47
  • public int compare(Foo o1, Foo o2) { return o1.sortOnMe < o2.sortOnMe ? -1 : o1.sortOnMe == o2.sortOnMe ? 0 : 1 ; } – Alexandr Jun 16 '11 at 09:48
  • @Alexandr You are right. Fixed it. I think I have to look through some code I wrote in the past 10 years or so now. Oh my... – Waldheinz Jun 16 '11 at 10:07
1

You can use Custom Comparator

See Also

Community
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jmj
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1

Simply write a class that implements Comparator-Interface.

Than use Collections.sort(list, comparator) to sort your List.

For more informations read this tutorial

CSan
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