Using StringComparato r

[wesomon99]

Hello.

I am using a StringComparato r to sort an ArrayList by a few different attributes. StringComparato r's compare(Object a, Object b) method takes two objects and returns an int value. This compare() method is automatically used by java's built-in sorting functionality.

The two objects I am using are called 'Submission's. I am trying to access attributes of each 'Submission' to sort from, but I don't know how to access 'Submission' methods when they must be passed simply as objects. I have tried casting them to (Submission)'s, but I get a class-casting error. Here is the pertinent code:

Method call from another class:

ArrayList scoringSet = DataObjectFactory.createScoringSet(fileStream, user);
Collections.sort(scoringSet, new StringComparator());
 

Method in StringComparato r class:

public final int compare (Object a, Object b)  {
 
    Submission sub1 = (Submission)a;
    Submission sub2 = (Submission)b;
 
    return sub1.getProblemIdx().compareTo(sub2.getProblemIdx());
}
 

So I need to access the problem_idx attribute, which I would normally do by calling Submission.getP roblemIdx(). However, it fails when attempting to cast a with '(Submission)a; '.

Any tips?

[prometheuzz]

....
'Submission' methods when they must be passed simply as objects. I have tried casting them to (Submission)'s, but I get a class-casting error. Here is the pertinent code:

Yes, casting them is good. But if you get a ClassCastExcept ion, it means there are other objects in your array then you think.
If you're using Java 1.5+, you can use generics so there is no need to cast:

class YourComparator implements Comparator<Foo> {
  public int compare(Foo f1, Foo f2) {
    // your code here
  }
}

If you keep having problems, could you then post a piece of code to replicates this behavior? There seems nothing wrong with the code you posted.