Sort an array of objects in Java

Question

I am working on a report module that shows the time spent and number of tasks. The values are set in the Java Bean and the bean object is stored in a array.I am using separate queries to get time and number of tasks.Now i have to sort the array based on time and number of tasks. The code below compares only Strings:

if (!list.isEmpty()) {
    Collections.sort(list, new Comparator<Project>() {
        @Override
        public int compare(Project p1, Project p2) {

            return p1.getName().compare(p2.getName());
        }
       });
   }

I have problems in sorting the integer value of a property in JavaBean which is stored in an array.Any help is greatly appreciated.

Are you tying to sort integer array, you can use `Arrays.sort(int[] a)` — Shivam, Feb 19 '13 at 09:26
`Integer` and `Date` both also have a `compareTo` method, can't you use them? — sp00m, Feb 19 '13 at 09:28
@Jason: Project[] array = new Project[3]; I am setting the integer value in a property of Project object and then I am storing the project object in the array. This is what you are asking, right? — santhosh, Feb 19 '13 at 09:38
why you should not storing project in the list ? That's easy to sort. — Jason, Feb 19 '13 at 09:46
@Jason: Ok i will try storing project in the list but for comparing the property the above logic can be used, right? — santhosh, Feb 19 '13 at 09:52
@santhosh you can refer to compare method, see this http://docs.oracle.com/javase/6/docs/api/java/util/Comparator.html — Jason, Feb 19 '13 at 09:55
@jlordo that's same for sort. But suggestion from effective java is "Prefer lists to arrays" — Jason, Feb 19 '13 at 10:00

score 7 · Accepted Answer · answered Feb 19 '13 at 09:53

In your comments below the question you say you have:

Project[] array = new Project[3];

If I were you I'd declare Project as

public class Project implements Comparable<Project> {

    @Override
    public int compareTo(Project other) {
        return this.id - other.id; // or whatever property you want to sort
    }

Then you can sort your array by simply calling

Arrays.sort(array);

If you don't want your class to implement the Comparable interface you can pass a comparator to Arrays.sort():

    Arrays.sort(array, new Comparator<Project>() {
        @Override
        public int compare(Project o1, Project o2) {
            return o1.id - o2.id; // or whatever property you want to sort
        }
    });

I used an anonymous one, you could also extract it to it's own class if needed elsewhere.

cowls · Answer 2 · 2013-02-19T09:59:21.690

0

How about something like:

Project[] project = ..initialise array;

List<Project> projectList = Arrays.asList(project);
Collections.sort(projectList, new Comparator<Project>() {
    @Override
    public int compare(Project p1, Project p2) {
        if(p1.getIntProperty() == p2.getIntProperty()) return 0;
        return p1.getIntProperty() > p2.getIntProperty() ? 1 : -1;
    }
   });
}

edited Feb 19 '13 at 09:59

answered Feb 19 '13 at 09:26

cowls

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what's happen if two values equal ? – Jason Feb 19 '13 at 09:28
2

And what if both values are equal? You never return `0`. – Rohit Jain Feb 19 '13 at 09:28
Updated, wouldve done the job anyway, but seems people dont like it not returning 0. Personally I like the 1 liner – cowls Feb 19 '13 at 09:32
Why convert it to a list, if you can simply sort the array? – jlordo Feb 19 '13 at 09:54
I based this on the OPs example of Sorting Strings, assuming he wished to do it the same way. I also think he may be dealing with a list anyway – cowls Feb 19 '13 at 09:59

score 0 · Answer 3 · answered Feb 19 '13 at 09:28

0

try this to sort integers

return(p1.getIntProperty() - p2.getIntProperty());

answered Feb 19 '13 at 09:28

codeMan

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score 0 · Answer 4 · edited May 23 '17 at 12:00

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Did you look into the Comparator and Comparable interfaces in java. You can use the compare() method to compare the elements in the array and sort them accordingly. You check this post where same question is already answerd Sort Java Collection

edited May 23 '17 at 12:00

Community

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answered Feb 19 '13 at 09:35

Swagatika

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score 0 · Answer 5 · edited Jun 26 '14 at 12:09

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You can pass a comparator to Arrays.sort():

Arrays.sort(array, new Comparator<Project>() {
    @Override
    public int compare(Project o1, Project o2) {
        return o1.id - o2.id; // or whatever property you want to sort
    }
});

edited Jun 26 '14 at 12:09

blalasaadri

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answered Jun 26 '14 at 11:48

Lenchik

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Johnny · Answer 6 · 2017-06-14T17:32:45.753

0

Assuming you have a List<Project>, all you need in Java8 (since you can use lambda expression for the Comparator) is:

Collections.sort(list, (o1, o2) -> o1.getName().compareTo(o2.getName()));

And List has a sort(Comparator) method, so you can shorten this even further:

list.sort((o1, o2) -> o1.getName().compareTo(o2.getName()));

With method references it becomes even cleaner:

list.sort(Comparator.comparing(Project::getName));

edited Jun 14 '17 at 17:32

answered Jun 14 '17 at 07:55

Johnny

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Who was using public fields? – shmosel Jun 14 '17 at 07:58
Assumptions. But you right, I edited the answer. Thanks. – Johnny Jun 14 '17 at 08:19
I'm still confused. All of your solutions use accessor methods. Did you mean method references? – shmosel Jun 14 '17 at 16:17

Sort an array of objects in Java

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