integer array static initialization

Question

Which two code fragments correctly create and initialize a static array of int elements? (Choose two.)

A.

static final int[] a = { 100,200 };

B.

static final int[] a;
static { a=new int[2]; a[0]=100; a[1]=200; }

C.

static final int[] a = new int[2]{ 100,200 };

D.

static final int[] a;
static void init() { a = new int[3]; a[0]=100; a[1]=200; }

Answer: A, B

here even D seems true, can anyone let me know why D is false.

Answer 1

The correct answers are 1 and 2 (or A and B with your notation), and an also correct solution would be:

static final int[] a = new int[]{ 100,200 };

Solution D doesn't initalize the array automatically, as the class gets loaded by the runtime. It just defines a static method (init), which you have to call before using the array field.

Answer 2

D defines a static method for initialising a but does not actually call it. Thus, a remains uninitialised unless someone explicitly calls the init method.

As other answers have pointed out: D shouldn't even compile because it attempts to assign a value to the final variable a. I guess that's a much more correct explanation. Nevertheless, even if a was not final D would still not work without extra code.

I assume the new int[3] in D is a typo? The other three all attempt to create an array of length 2.