Notes _ _ fat Interface Segregation Principle Interface

namespace the Test {
     / * fat exemplary interfaces * / 
    public  class Program {
         static  void the Main ( String [] args) {
             int [] = {nums1 . 1 , 2 , . 3 , . 4 , . 5 };
            ArrayList nums2 = new ArrayList { 1, 2, 3, 4, 5 };
            var nums3 = new ReadOnlyCollection(nums1);
            Console.WriteLine(Sum(nums1));
            Console.WriteLine(Sum(nums2));
            Console.WriteLine(Sum(nums3));

            Console.Read();
        }

        // This interface is too fat, more demand, we actually need is foreach iteration function, so IEnumerable enough
         // static int Sum (ICollection nums)   
        static  int Sum (IEnumerable nums) {
             int SUM = 0 ;
             foreach ( var the n- in nums)
                sum += (int)n;
            return sum;
        }
    }

    public class ReadOnlyCollection : IEnumerable {
        private int[] _array;
        public ReadOnlyCollection(int[] array) {
            this._array = array;
        }
        public IEnumerator GetEnumerator() {
            return new Enumerator(this);
        }

        public class Enumerator : IEnumerator {
            private ReadOnlyCollection _collection;
            private int _head;
            public Enumerator(ReadOnlyCollection collection) {
                this._collection = collection;
                _head = -1;
            }
            public object Current {
                get {
                    object o = _collection._array[_head];
                    return o;
                }
            }
            public bool MoveNext() {
                if(++_head < _collection._array.Length) {
                    return true;
                }
                else {
                    return false;
                }
            }
            public void Reset() {
                _head = -1;
            }
        }
    }
}