varargs in java | variable arity parameter in java | variable arity method in java

In this video you will learn what is variable arity parameter and what is varargs in java.

A fixed arity method must be called with the same number of actual parameters (also called arguments) as the number of formal parameter specified in its declaration.
If the method declaration specifies two formal parameters, every call of method must specify exactly two arguments. We say that the arity of this method is 2.
In other words arity of such a method is fixed, and it is equal to the number of formal parameters specified in the method declaration.

Java also allows declaration of variable arity methods; meaning that the number of arguments in its call can be varied.

Invocation of such a method may contain more actual parameters than formal parameters.

The variable arity parameter in method declaration is represented by the …(ellipsis).
It have following syntax:

return-type methodname(type… parameter-name)
{
}

The ellipsis(…) is specified between type and the formal parameter name.
The type can be a primitive data-type , a reference type.
Whitespaces can be specified on both sides of ellipsis.
Such a parameter is called a varargs parameter.
Apart from the vararg parameter , a variable arity method is identical to a fixed arity method.

The method show() below is a variable arity method:

public void show(int … x)
{ for(int y:x)
{ System.out.println(y);
}
}

The vararg parameter in a variable arity method is always interpreted as array. So in method show() x is treated as a simple array of integers.
Only one vararg parameter is permitted in the formal parameter list, and it is always the last parameter in the formal parameter list.
Given that the method declaration have n formal parameters, and the method call has k actual parameters, k must be equal to or greater than n-1.
The last k-n+1 actual parameter are evaluated and stored in an array whose reference value is passed as the value of actual parameter.

Calling a varargs method

show(10,20);
show();
show(10,20,30,40,50);

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