用Java定义一个String数组

Question

In java we can define main() method as both these ways.

public static void main(String[] args) {          
    System.out.println("Hello World");
}

.

public static void main(String... args) {          
    System.out.println("Hello World");
}

Both method takes array of String arguments. Now consider following scenario.

    String[] arr=new String[10]; // valid
    String... arr=new String[10];// invalid 

Java never allows to create an array like this way String... arr=new String[10]; . But in above method implementation java allows to do so. My question is how java achieve this two different behavior for two scenarios?

Answer 1

... 

is a syntax for method arguments and not for variable definitions. The name of this notation is varargs , which is self explanatory ie variable number of arguments.

Answer 2

Java中的可变参数或varargs（...）用于编写更灵活的方法，这些方法可以接受不需要初始化的任意数量的参数。

Answer 3

... refers to varargs and its main intention to make method more readable .

void method(String... args) {

}

can be called as

method("a"); OR method("a", "b"); OR method("a", "b", "c");

I see no point in using it in variable declaration, we can't do much with

String... a = {"a", "b"}

An array can anyways be declared with dynamic size

String[] arr = {"a"};

OR

String[] arr = {"a", "b"};

Answer 4

You can use varargs in main because a method declared with varargs (...) is bytecode compatible with a declaration of a method with an array argument (for backwards compatibility). That does not mean that the same syntax is allowed for type declarations.