问题
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.
回答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.
回答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.
回答3:
D (4) is false, because a) a is final and you cannot assign it in init; b) there is no guarantee that init will be called; c) init doesn't set the third element;
回答4:
for snippet C You cannot give dimensions ( Size ) while initializing for snippet D you should initialize final variable. It cannot be initialized later.
回答5:
final variables should be initialized before constructor call completes. Since "static void init()" is a method & it will not run before constructor, final variables won't be initialized. Hence it is an compile time error.
来源：https://stackoverflow.com/questions/4449935/integer-array-static-initialization