Question

Okay suppose I have an array of objects that look like this:
obj(from, to)
I want to to sort that array by comparing from and to. An example of what I want done:
Suppose I have objects with these parameters
(0,2) (2,4) (0,3) (4,5) (2,3)
I want the objects to be sorted in this order:
(0,2) (0,3) (2,3) (2,4) (4,5)

I want the first two “from” variables compared and the lower one placed in front. If they are equal then I want the second pair of number compared. To do this I created a compare method

public int compare (EdgeI e1, EdgeI e2) {
  if(e1.from < e2.from) { return -1; }
  else if(e1.from == e2.from) {
    if(e1.to < e2.to) { return -1; }
    else if(e1.to == e2.to) { return 0; }
    else if(e1.to > e2.to) { return 1; }
  }
  return 1;
}

Would this work? And if so, how would I run this sort through the array?
Thanks for any help.

EDIT

    public class mySorter implements Comparator <EdgeI> {

  public int compare(EdgeI e1, EdgeI e2) {
    if(e1.from < e2.from) { return -1; }
    else if(e1.from == e2.from) {
      if(e1.to < e2.to) { return -1; }
      else if(e1.to == e2.to) { return 0; }
      else if(e1.to > e2.to) { return 1; }
    }
    return 1;
  }

  public void sorterM () {
    Collections.sort(tet2, new mySorter());
  }

}

I get the error Collections cannot be resolved, and tet2 cannot be resolved. Tet2 is a List delcared public in another class.

Answer 1

What you can do is create a class which implements Comparator<Edge>. You can then use your compare method to implement the method from the interface.

After you have done this you can use the comparator to sort a list of Edge objects using Collections.sort().

This would look something like this:

import java.util.Collections;
import java.util.List;
import java.util.Comparator;

public class EdgeComparator implements Comparator<Edge> {
    public int compare(Edge l, Edge r) { ... }
}

void yourCode() {
    List<Edge> edges = ...;
    Collections.sort(edges, new EdgeComparator());
    //edges now contains the sorted edges
}

Here is the javadoc on Comparator and Collections.sort.

If you have an array instead of a list you can instead use Array.sort in the same way as Collections.sort.