sort arraylist of object from different class

Assuming these objects are of type Foo which does not implement Comparable<Foo> but does have a method public int getBar(), you can pass your own Comparator<Foo> to Collections#sort() like so:

List<Foo> foos = /* whatever */;
Collections.sort(foos, new Comparator<Foo> () {
   @Override
   public int compare(Foo a, Foo b) {
       return Integer.compare(a.getBar(), b.getBar());
   } 
});

Note that Integer#compare(int, int) is only since Java 7. If you're using anything older, use this implementation instead:

   public int compare(Foo a, Foo b) {
       int x = a.getBar();
       int y = b.getBar();

       return (x < y) ? -1 : ((x == y) ? 0 : 1);
   } 

This is exactly how Integer#compare() works internally.

Use Comparator for this issue.

Assume that shared method is public Integer sharedMethod() then do the sorting as below:

    List<SharedClass> list = new ArraList<SharedClass>();
    ....

    //Sorting here
    Collections.sort(list, new Comparator<SharedClass>(){
      @Override
      public int compare(SharedClass sc1, SharedClasssc2){
          return sc1.sharedMethod().compareTo(sc1.sharedMethod());
      }
     });

If it is returns int then use Integer.compare method (Java7) as below:

    //Sorting here
    Collections.sort(list, new Comparator<SharedClass>(){
      @Override
      public int compare(SharedClass sc1, SharedClasssc2){
          return Integer.compare(sc1.sharedMethod(), sc1.sharedMethod());
      }
     });

If using Java Version below 7, then:

    //Sorting here
    Collections.sort(list, new Comparator<SharedClass>(){
      @Override
      public int compare(SharedClass sc1, SharedClasssc2){
          int value1 = sc1.sharedMethod();
          int value2 = sc1.sharedMethod();
          //return 1, if value1 is greater,-1 if smaller and 0 if equal to value2. 
          return (value1  < value2) ? -1 : ((value1 > value2) ? 1 : 0);
      }
     });