Question

I have an array of objects populated by a .txt file

Object[] punteggiTutti = scores.toArray();

Even if it’s possible to use the .sort function:

Arrays.sort(punteggiTutti, Collections.reverseOrder());

I would know how to apply a working bubblesort algorithm; I tried the following not working code:

for(int i=0; i<j; i++) 
    {
    if(punteggiTutti[i]<punteggiTutti[i+1])  // error "<" operator cannot be used in objects 
      {
      temp=punteggiTutti[i]; 
      punteggiTutti[i]=punteggiTutti[i+1];
      punteggiTutti[i+1]=temp;
      }
    }

Answer 1

You can’t compare two Objects with < operator.

Use something which implements Comparable interface. Then such elements can be compared using function a.compareTo(b);

http://download.oracle.com/javase/1.5.0/docs/api/java/lang/Comparable.html

Also have a look at:
http://leepoint.net/notes-java/data/expressions/22compareobjects.html

Try to read about equality in Java. This should help you with future errors when using Java.