Sorting objects of different types into one list

Question

I have the following problem and I'm not quite sure how to go about solving it. I am requesting data from several different servers with each server returning a list of objects of a different type (every server has it's own specific unique POJO object type) - but what all these lists of objects have in common is that all the objects have a date parameter. I then need to display the objects from all the lists as one huge mixed list for the user, with all the various objects sorted by date.

I made an adapter that extends baseadapter and I've passed all the arraylists of objects to that adapter - but how can I sort all these lists of objects by date and display them all together? I could create a "super object" that has the properties of all the other objects and then make one sorted array of this super object to pass to the adapter, but that seems like a messy and crude solution. Is there a more or less elegant way to do this?

public class someAdapter extends BaseAdapter
{
...

public someAdapter(ArrayList<ObjectOne> objectOneArray, ArrayList<ObjectTwo> objectTwoArray) {
        if (objectOneArray != null) {
            this.localObjectOneList.addAll(objectOneArray);
        }
        ...
}
}

Example of an object type:

public class ObjectOne implements Serializable {
private String date;
private String someFieldOne;
private String someFieldTwo;

...
//getters and setters
...
}

To reiterate - the final list has to be a mix of all the different object types in the order of their dates.

Answer 1

The way you expected initially to have a super class would be nice if there weren't a huge plumbing associated. A better approach can be as follows: Assuming that all the POJOs have getDate() method.

1. Declare a method getDate() to retrieve date object from any POJO.
2. Declare a Comparator to compare dates

3. Sort the objects

   If the POJOs don't have getters i.e, getDate() method, replace getDateFromMethod() with getDateFromProperty() in the comparator .

   public class Sorter{ public void sortList()
   {
       Collections.sort(objList, comparator);
   
       // Now consume / print your objList to get sorted by date
   }
   
   ArrayList<Object>   objList     = new ArrayList<Object>();
   
   Comparator<Object>  comparator  = new Comparator<Object>()
                                   {
   
   
   
                                   @Override
                                   public int compare(Object object1, Object o2)
                                       {
                                           Date o1Date = getDateFromMethod(object1);
                                           Date o2Date = getDateFromMethod(o2);
                                           if (o1Date != null && o2Date != null)
                                           {
                                               if (o1Date.before(o2Date))
                                                   return -1;
                                               else if (o1Date.after(o2Date))
                                                   return 1;
   
                                               else
                                                   return 0;
                                           }
                                           else
                                               return -1;
                                       }
                                   };
   
   public Date getDateFromMethod(Object obj)
   {
   
       Date date = null;
       String getDate = "getDate";
       try
       {
           Method method = obj.getClass().getMethod(getDate, (Class<?>[]) null);
           if (method != null)
               date = (Date) method.invoke(obj, (Object[]) null);
       }
       catch (NoSuchMethodException e)
       {
           // TODO Auto-generated catch block
           e.printStackTrace();
       }
       catch (SecurityException e)
       {
           // TODO Auto-generated catch block
           e.printStackTrace();
       }
       catch (IllegalAccessException e)
       {
           // TODO Auto-generated catch block
           e.printStackTrace();
       }
       catch (IllegalArgumentException e)
       {
           // TODO Auto-generated catch block
           e.printStackTrace();
       }
       catch (InvocationTargetException e)
       {
           // TODO Auto-generated catch block
           e.printStackTrace();
       }
   
       return date;
   }public Date getDateFromProperty(Object obj)
                               {
                                   Date date=null;
                                   try
                                   {
                                   Field dateField=    obj.getClass().getField("date");
                                   if(dateField!=null)
                                       date=(Date) dateField.get(obj);
                                   }
                                   catch (NoSuchFieldException e)
                                   {
                                       // TODO Auto-generated catch block
                                       e.printStackTrace();
                                   }
                                   catch (SecurityException e)
                                   {
                                       // TODO Auto-generated catch block
                                       e.printStackTrace();
                                   }
                                   catch (IllegalArgumentException e)
                                   {
                                       // TODO Auto-generated catch block
                                       e.printStackTrace();
                                   }
                                   catch (IllegalAccessException e)
                                   {
                                       // TODO Auto-generated catch block
                                       e.printStackTrace();
                                   }
   
                                   return date;
   
                               }
   

   }

   Now say for instance you have Obj1,Obj2 and Obj3 as follows, create objects using these POJOS and populate the objList and test the solution.

class Obj1 { int id; int name; Date date;

public Date getDate()

{ return date; } public int getId() { return id; }

public void setId(int id)
{
    this.id = id;
}

public int getName()
{
    return name;
}

public void setName(int name)
{
    this.name = name;
}

}

class Obj2 { int sequence; int location; Date date;

public Date getDate()

{ return date; } public int getSequence() { return sequence; }

public void setSequence(int sequence)
{
    this.sequence = sequence;
}

public int getLocation()
{
    return location;
}

public void setLocation(int location)
{
    this.location = location;
}

}

class Obj3 { int type; int origin; Date date;

public Date getDate()

{ return date; }

public void setDate(Date date) { this.date = date; }

public int getType()
{
    return type;
}

public void setType(int type)
{
    this.type = type;
}

public int getOrigin()
{
    return origin;
}

public void setOrigin(int origin)
{
    this.origin = origin;
}

}

Answer 2

You can create your own interface with method getDate()

interface PojoInterface {
    ...
    Date getDate();
}

every POJO should implement this interface

then you should create your custom Comparator class

class CustomComparator implements Comparator<PojoInterface> {

    @Override
    public int compare(PojoInterface a, PojoInterface t1) {
        return a.getDate().compareTo(t1.getDate());
    }

    ...
}

and then sort one general list

public someAdapter(ArrayList<A> objectOneArray, ArrayList<A> objectTwoArray) {
    this.localObjectsList.addAll(objectOneArray);
    this.localObjectsList.addAll(objectTwoArray);
    Collections.sort(this.localObjectsList, new CustomComparator());
    ...
}

Answer 3

If you are able to change the class definition of the objects, I suggest you let them implement Comparable, and then override the compareTo() method, then finally use Arrays.sort() to sort the list

Answer 4

Just Use the List of Object Type to Hold any Reference type

List<Object> localObjectOneList= new ArrayList <Object>();