Question

Simple java ques about addition in array in a loop:

//sum the elements in an array
public static void loop7()
{
int[] numbers = {2,3,4,5,6,7,8,9,10};
int sum = 0;
for (int i = 0; i < numbers.length; ++i)
{
sum = sum + numbers[i];
}
System.out.println("The sum of the array is " + sum);

Why is it, that when we are adding we say:
sum = sum + numbers[i];
and not:
sum = numbers[i];
?