[英]integer array static initialization
Which two code fragments correctly create and initialize a static array of int elements? 哪两个代码片段正确创建并初始化int元素的静态数组? (Choose two.) (选择两个。)
A. 一个。
static final int[] a = { 100,200 };
B. B.
static final int[] a;
static { a=new int[2]; a[0]=100; a[1]=200; }
C. C。
static final int[] a = new int[2]{ 100,200 };
D. D.
static final int[] a;
static void init() { a = new int[3]; a[0]=100; a[1]=200; }
Answer: A, B 答案:A,B
here even D seems true, can anyone let me know why D is false. 这里甚至D似乎都是真的,任何人都可以让我知道为什么D是假的。
The correct answers are 1 and 2 (or A and B with your notation), and an also correct solution would be: 正确的答案是1和2(或带有您的符号的A和B),一个正确的解决方案是:
static final int[] a = new int[]{ 100,200 };
Solution D doesn't initalize the array automatically, as the class gets loaded by the runtime. 解决方案D不会自动初始化数组,因为运行时会加载类。 It just defines a static method (init), which you have to call before using the array field. 它只定义了一个静态方法(init),在使用数组字段之前必须调用它。
D defines a static method for initialising a
but does not actually call it. D定义了一个静态方法来初始化a
但实际上并没有调用它。 Thus, a
remains uninitialised unless someone explicitly calls the init
method. 因此, a
遗体未初始化的,除非有人明确地调用init
方法。
As other answers have pointed out: D shouldn't even compile because it attempts to assign a value to the final
variable a
. 正如其他答案所指出的那样:D甚至不应该编译,因为它试图为final
变量a
赋值。 I guess that's a much more correct explanation. 我想这是一个更正确的解释。 Nevertheless, even if a
was not final D would still not work without extra code. 然而,即使a
没有最终d仍然没有额外的代码工作。
I assume the new int[3]
in D is a typo? 我假设D中的new int[3]
是拼写错误? The other three all attempt to create an array of length 2. 其他三个都试图创建一个长度为2的数组。
D (4) is false, because a) a
is final and you cannot assign it in init
; D(4)是假的,因为a) a
是最终的,你不能在init
分配它 ; b) there is no guarantee that init
will be called; b)无法保证会调用init
; c) init
doesn't set the third element; c) init
不设置第三个元素;
for snippet C You cannot give dimensions ( Size ) while initializing for snippet D you should initialize final variable. 对于片段C您在初始化片段D时不能给出尺寸(大小),您应该初始化最终变量。 It cannot be initialized later. 它无法在以后初始化。
final variables should be initialized before constructor call completes. 应该在构造函数调用完成之前初始化最终变量。 Since "static void init()" is a method & it will not run before constructor, final variables won't be initialized. 由于“static void init()”是一个方法,它不会在构造函数之前运行,因此最终变量不会被初始化。 Hence it is an compile time error. 因此它是编译时错误。
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