What is the difference between String[] and String... in Java?

Question

How should I declare main() method in Java?

Like this:

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

Or like this:

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

What's actually the difference between String[] and String... if any?

Answer 1

How should I declare main() method in Java?

String[] and String... are the same thing internally, i. e., an array of Strings. The difference is that when you use a varargs parameter (String...) you can call the method like:

public void myMethod( String... foo ) {     // do something     // foo is an array (String[]) internally     System.out.println( foo[0] ); }  myMethod( "a", "b", "c" );  // OR myMethod( new String[]{ "a", "b", "c" } );  // OR without passing any args myMethod(); 

And when you declare the parameter as a String array you MUST call this way:

public void myMethod( String[] foo ) {     // do something     System.out.println( foo[0] ); }  // compilation error!!! myMethod( "a", "b", "c" );  // compilation error too!!! myMethod();  // now, just this works myMethod( new String[]{ "a", "b", "c" } ); 

What's actually the difference between String[] and String... if any?

The convention is to use String[] as the main method parameter, but using String... works too, since when you use varargs you can call the method in the same way you call a method with an array as parameter and the parameter itself will be an array inside the method body.

One important thing is that when you use a vararg, it needs to be the last parameter of the method and you can only have one vararg parameter.

You can read more about varargs here: http://docs.oracle.com/javase/1.5.0/docs/guide/language/varargs.html

Answer 2

String... gets converted to a String[]. The main difference is that you can call a vararg method in 2 ways:

method(a, b, c); method(new String[] {a, b, c}); 

whereas you need to call a method that accepts an array like this:

method(new String[] {a, b, c}); 

For the main method it does not make a difference.