Is a variable length argument treated as an array in Java?

Question

As I understand an array consists of fixed number of elements and a variable length argument takes as many number of arguments as you pass (of the same type). But are they same? Can I pass one where the other is expected?

Answer 1

Yes, if you have a method with a varargs parameter like this:

public void foo(String... names)

and you call it like this:

foo("x", "y", "z");

then the compiler just converts that into:

foo(new String[] { "x", "y", "z"});

The type of the names parameter is String[], and can be used just like any other array variable. Note that it could still be null:

String[] nullNames = null;
foo(nullNames);

See the documentation for varargs for more information.

This does not mean that varargs are interchangeable with arrays - you still need to declare the method to accept varargs. For example, if your method were declared as:

public void foo(String[] names)

then the first way of calling it would not compile.

Answer 2

They are the same, array is internally used by JVM when creating varargs methods. So you can treat vararg argument in the same way you treat array so use for instance enhanced for loop

public void method(String... args) {
    for(String name : args) {
     //do something
     }
}

and call it like this or even pass an array

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

See this nice article for further explanation.

Answer 3

A simple test would suggest that they are the same:

public class test {

    public static void varArgs(String... strings) {
        for (String s : strings) {
            System.out.println(s);
        }
    }

    public static void main(String[] args) {
        String[] strings = {"string1", "string2", "string3"};
        varArgs(strings);
        varArgs("string4", "string5", "string6");
    }
}

Outputs:

string1
string2
string3
string4
string5
string6