Interview street Median challenge
An additional point to the ones mentioned by @palacsint is the check for the object removal:
according to the challenge:


  If the operation is remove and the number x is not in the list, output
  "Wrong!" in a single line


your code does not check for that: here is what you have:

if(items.size()&lt;=1)
            {
              result[i]=-1;
            }
else .....


You are marking wrong when the list has a single item or is empty. Obviously this is not what the challenge requires. Therefore, you should discard this "if" block and only check the return value from the remove on the list:

boolean ok= items.remove((Integer)x[i]);
if (!ok){
  result[i]=-1;
}