Passing Information to a Method or a Constructor (The Java™ Tutorials > Learning the Java Language > Classes and Objects)

Passing Information to a Method or a Constructor (The Java™ Tutorials > Learning the Java Language > Classes and Objects): "Arbitrary Number of Arguments
You can use a construct called varargs to pass an arbitrary number of values to a method. You use varargs when you don't know how many of a particular type of argument will be passed to the method. It's a shortcut to creating an array manually (the previous method could have used varargs rather than an array)."

Arbitrary Number of Arguments

You can use a construct called varargs to pass an arbitrary number of values to a method. You use varargs when you don't know how many of a particular type of argument will be passed to the method. It's a shortcut to creating an array manually (the previous method could have used varargs rather than an array).

To use varargs, you follow the type of the last parameter by an ellipsis (three dots, ...), then a space, and the parameter name. The method can then be called with any number of that parameter, including none.

public Polygon polygonFrom(Point... corners) {
   int numberOfSides = corners.length;
   double squareOfSide1, lengthOfSide1;
   squareOfSide1 = (corners[1].x - corners[0].x)*(corners[1].x - corners[0].x)
   + (corners[1].y - corners[0].y)*(corners[1].y - corners[0].y) ;
   lengthOfSide1 = Math.sqrt(squareOfSide1);
   // more method body code follows that creates
   // and returns a polygon connecting the Points
}

You can see that, inside the method, corners is treated like an array. The method can be called either with an array or with a sequence of arguments. The code in the method body will treat the parameter as an array in either case.

You will most commonly see varargs with the printing methods; for example, this printf method:

public PrintStream printf(String format, Object... args)

allows you to print an arbitrary number of objects. It can be called like this:

System.out.printf("%s: %d, %s%n", name, idnum, address);

or like this

System.out.printf("%s: %d, %s, %s, %s%n", name, idnum, address, phone, email);

or with yet a different number of arguments.