Comparing Long values using Collections.sort(object)

Question

I'm trying to sort a simple list of objects by a long - the below isn't working because one of the long strings is pushed to the top simply because it starts with a lower number. So I'm looking for a way to sort these by the actual long values directly

The current obj implementation looks something like the below. In the class I'm using this I call Collections.sort(trees);

public class Tree implements Comparable<Tree> {
    public String dist; //value is actually Long

    public int compareTo(Tree o) {
        return this.dist.compareTo(o.dist);
    }
}

Answer 1

Long.compare( x , y )

If you have an object that you want to sort on a long value, and it implements Comparable, in Java 7+ you can use Long.compare(long x, long y) (which returns an int)

E.g.

public class MyObject implements Comparable<MyObject> {   public long id;    @Override   public int compareTo(MyObject obj) {     return Long.compare(this.id, obj.id);   } } 

Call Collections.sort(my_objects) where my_objects is something like

  List<MyObject> my_objects = new ArrayList<MyObject>();   // + some code to populate your list 

Answer 2

why not actually store a long in there:

public class Tree implements Comparable<Tree> {     public long dist; //value is actually Long      public int compareTo(Tree o) {         return this.dist<o.dist?-1:                this.dist>o.dist?1:0;     } } 

that or first compare the length of the strings and then compare them

public String dist; //value is actually Long public int compareTo(Tree o) {     if(this.dist.length()!=o.dist.length())           return this.dist.length()<o.dist.length()?-1:1;//assume the shorter string is a smaller value     else return this.dist.compareTo(o.dist); } 

Answer 3

well if the dist variable is actually long then you might try using

public int compareTo(Tree o) {
    return Long.valueOf(this.dist).compareTo(Long.valueOf(o.dist));
}

Answer 4

Just an example I made for sorting Files by date using a Long comparator:

public File[] getAllFoldersByDescendingDate(File folder) {
    if (!folder.isDirectory()) {
        return null;
    }
    allFiles = folder.listFiles();
    Arrays.sort(allFiles, new Comparator<File>()
    {
        public int compare(final File o1, final File o2)
        {
            return Long.compare(o2.lastModified(), o1.lastModified());
        }
    });
    return allFiles;
}