Casting from type object to a class

I'm currently t开发者_StackOverflow社区rying to populate an array of of objects of the type Stipulations which is a class which is an

public abstract interface

My method of populating this array is as follows where popStipAttr is a simple switch statement.

    public static Stipulations[] popStipArr(ZASAllocation zasAlloc) 

    {
          //ArrayList<String> s = new ArrayList<String>();
          ArrayList<Stipulations> stipAL  = new ArrayList<Stipulations>();

          for(int i = 0; i < NoStip; i++)
          {
          stipAL.add(popStipAttr(i,zasAlloc));
          }

          Stipulations[] StipArr =  (Stipulations[]) stipAL.toArray();
          return StipArr;
    }

However I get the error about casting:

Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Lc.Stipulations;

What exactly am I doing wrong here I created the arraylist of the same type, why would coverting it to an array of that type throw this?

---

ArrayList.toArray returns an Object[] (which, as stated in the message, can't be cast to Stipulations[]). ArrayList.toArray(T[] a) however, returns a T[]. Thus, change

Stipulations[] StipArr =  (Stipulations[]) stipAL.toArray();

to

Stipulations[] StipArr =  (Stipulations[]) stipAL.toArray(new Stipulations[0]);
                                                          ^^^^^^^^^^^^^^^^^^^

---

Oh, right. Just realized what may have caused the confusion. The leading [ in [Ljava.lang.Object; indicates that it is an array. Same for [Lc.Stipulations;. Perhaps that's why you wrote Casting from type object to a class as title :-) Now you know anyway :-)

---

What you are doing in

Stipulations[] StipArr =  (Stipulations[]) stipAL.toArray();

is calling the method on the java.util.List class

Object[] toArray(); 

which is returning you an Object[] which cant be cast to your Stipulations[]
What you want to be calling is the method on java.util.List

<T> T[] toArray(T[] a);

which will return you the array with your type. So try

Stipulations[] StipArr =  stipAL.toArray(new Stipulations[stipAL.size()]);

It is a strange syntax which tends to pollute the code and for this reason and a few others I always try to use Lists where possible and never convert to and from Arrays unless absolutely necessary like an external API not under my control requires it