Final answer:
In Java, attempting to access an array element with an out-of-bounds index results in an ArrayIndexOutOfBoundsException. This is a kind of runtime error that indicates an illegal index access in an array.
Step-by-step explanation:
If an array does not exist or an element is accessed with an index that is out of the bounds of the array, the Java runtime system will indeed throw an ArrayIndexOutOfBoundsException. This exception is a runtime error, meaning it happens during the program's execution when the problematic code is reached. The Java runtime environment checks array accesses to ensure that the index used is within the valid range of the array, which starts at 0 and goes up to the array's length minus one. If the index is negative or it is not less than the array's length, the Java runtime throws an ArrayIndexOutOfBoundsException.
For example:
int[] numbers = new int[3]; // Array of 3 elements
numbers[3] = 4; // This will throw ArrayIndexOutOfBoundsException because there is no index 3 in an array of 3 elements (0, 1, 2).
It's important to note that checking for the existence of the array before using it can prevent a NullPointerException, which is different from ArrayIndexOutOfBoundsException.