Java中两个数组声明之间有什么区别？

Question

In my book they've been switching the way the declare arrays between the following two methods:

    int array1[] = {1, 2, 3};
    int[] array2 = {1, 2, 3};

I was wondering what the difference was between the positioning of the two brackets, and why is it that when I put the brackets after the name (such as in array 1), why I must either initialize it to a set of values or a new array, but in array2, I can simply say "int[] array2;" and then use it later...?

Answer 1

They are identical except that as you mention you have to initialize it if you put the brackets after the name. One advantage of declaring them before the name is multiple array initialization like this:

int [] myArray1, myArray2;

int myArray1[], myArray2[];

The Java way according to the documentation is to put the brackets before the array name.

Answer 2

There is no difference between them as they both declare a variable of type "array of ints". There is no "Java way" (but a preferred way), even if the documentation, arrays are declared with brackets before the variable name :

int[] array1;

Note : Pay attention that "declaration" is not "initialisation" (or instanciation )

int[] array1;   // declares an array of int named "array1"
                // at this point, "array1" is NOT an array, but null
                // Thus we "declare" a variable that will hold some 
                // data of type int[].

array1 = new int[] {1, 2, 3};   // legacy initialization; set an array of int
                                // with 3 values to "array1". Thus, we "initialize"
                                // the variable with some data of type int[]

Therefore,

int [] array1;
int array2[];

both declares two variables of type int[] ; however, they are just declarations of data types, and not arrays yet. And like Oscar Gomez said, the difference now is that the second "way" requires you to specify that the variable is of type array, and not only an int.

int i[], j;   // i is a data type array of int, while j is only an int
int [] k, l;  // both k and l are of the same type: array of int

Answer 3

An array is created by an array creation expression or an array initializer . The former applies to array2 ( although in this case, an array initializer was provided ), whereas the latter applies to array1 .

For more information, see:

• JLS, §10.3 - Array Creation
• JLS, §10.6 - Array Initializers
• JLS, §15.10 - Array Creation Expressions