The difference between String [] a and String ... a

Question

What is the difference when we write String [] a in the main method and String ... a?

public static void main(String[]a) 

and

 public static void main(String...a) 

Answer 1

The first expects one parameter, which is an array of strings.

The second takes zero or more String parameters. It also accepts an array of strings.

Answer 2

 public static void main(String[] a) 

This should be called with a single argument of type String [] or null.

 public static void main(String...a) 

This call can be called with a single argument of type String [], OR with any number of String arguments, for example main ("a", "b", "c"). However, the compiler will complain if you pass null, as it cannot determine if you have a String [] value of null or an array of 1 null string.

Inside main() in any case, the variable a is equal to String[] .

Since this is main , you may not think about what it will be called ... Usually this is the first. But I switched to using the second form for all my networks; it is easier to pass arguments for testing.

Answer 3

The second is called varargs and was introduced in Java 5. It frees you from explicitly creating an array when you need to go to zero or more parameters to a method.