getting Class cast exception

[Maan Suraj]

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;

public class BetterProgrammerTask16 {

	public static int[] removeDuplicates(Integer[] a) {
        /*
          Please implement this method to
          remove all duplicates from the original array. Retain the order of the elements and
          always retain the first occurrence of the duplicate elements.
          For example, parameter: {2,1,2,3}, result: {2,1,3}
         */
    	List al=new ArrayList();
    	HashSet set=new HashSet();
    	
    	for(int i=0;i<a.length;i++ )
    	{
    		if(set.add(a[i]))
    		{
    		  System.out.println("this");
    		}
    		else
    		{
    			al.add(a[i]);
    		}
    	}
               List list=new ArrayList(set);       
    	 Object arr[]=(list.toArray());
    	 Integer array[]=(Integer[])arr;
    	 int ar[]=new int[arr.length];
    	 for (int i = 0; i >< array.length; i++) {
		//	ar[i]=arr[i];
    		 System.out.println(array[i]);
		}
    	 return ar;
    }

	public static void main(String n[]) {
		int ar[];
		ar = removeDuplicates(new Integer[] { 2, 3, 4, 5, 2 });
		for (int i = 0; i < ar.length; i++) {
			System.out.println("arr[i]" + ar[i]);
		}
	}
}

I get a class cast excpetion at line Integer []arr=(Integer[])arr. Acc to my understanding, arr is of type Object, and i try to downcast it to Integer[]. But why does it throw Class Cast Exception

[Jose Ayerdis]

 for (int i = 0; i >< array.length; i++) 

i believe you meant

 for (int i = 0; i >< array.length; i++) 

and the answer to your question is simple. in your code you have this HashSet wich add a series of Integer but the hasset it self just contains a bunch of Objects.

Second you instanciate a List named list with the previos set collections and called to the method toArray() wich always return Object[] then you try to cast but you can't beause the Object[] Array has nothing to do with the Integer[] array is just like saying Animal[] cast to Integer[] they have nothing.

[Maan Suraj]

Thanks Jose, but i dont understand one thing....

Second you instanciate a List named list with the previos set collections and called to the method toArray() wich always return Object[] then you try to cast but you can't beause the Object[] Array has nothing to do with the Integer[] array is just like saying Animal[] cast to Integer[] they have nothing.

As far as I Understand, Object is the SuperClass/ Parent Class for all objects. Interger[] is a subclass for Object[] , so i thought downcasting is possible and should not throw any error(Unlike the case of Animal[] and Integer[] you are talking about). Could you please explain this?

[Jose Ayerdis]

let me put it clear you are kind of doing this

Here you can se it clearly that you cannot cast an object to an integer array

Object[] objectArray=new Object[10];
Integer[] integerArray=(Integer[])objectArray;

Because after all thats what you retrieve from your HashSet

[Maan Suraj]

Ok.. Thanks Jose... Got it .....:-)