Vararg

Vararg: arguments in variable quantity

• Some methods may need a variable number of arguments, depending on your application.

• An example is a method that opens an Internet connection and can receive parameters such as username, password, filename, protocol, etc.

• If some information is not passed, the method can use defaults for those parameters.

• Methods with variable length arguments allow passing only the necessary arguments.

• Before JDK 5, these methods were handled with overloading or arrays, which was a limited and clumsy approach.

• Starting with JDK 5, the varargs feature was introduced, which makes it easier to create methods with a variable number of arguments.

• Vararg is short for "variable-length arguments".

• Methods that use varargs are called variable arity methods or simply varargs methods.

• The parameter list of a varargs method is of variable length, allowing it to receive a variable number of arguments.

Basic aspects of varargs

• A variable-length argument list is specified by three dots (...).

• To create a method that receives a variable number of arguments, use these three points in the method declaration.

• An example is the vaTest() method, which demonstrates how to implement this functionality.

• Note that v is declared as: int ... v

• The syntax with ... tells the compiler that vaTest() can be called with zero or more arguments.

• The parameter v is implicitly declared as an array of type int[].

• Within the vaTest() method, v is accessed using common array syntax.

• A complete program can demonstrate the use of vaTest().

• Within vaTest(), the parameter v is treated as an array because it is, in fact, an array.

• The ... syntax tells the compiler that a variable number of arguments will be used, which will be stored in the array v.

• In the main() method, vaTest() is called with different numbers of arguments, including none.

• When there are no arguments, the array v has size zero.

• Methods can have common parameters along with variable-length parameters, but varargs must be the last one declared.

• Example of acceptable declaration: int doIt(int a, int b, double c, int ... vals).

• In this case, the first arguments are passed to common parameters, and the rest to vals.

• The vaTest() method can be rewritten to take a common argument in addition to varargs.

• The varargs parameter must be the last one in the method parameter list.

• It is not allowed to declare a common parameter after a varargs parameter; this generates an error.

• Only one varargs parameter can be declared in a method.

• Trying to declare more than one varargs parameter in the same method, as in int ... vals followed by double ... morevals, is invalid and generates an error.

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