variable-length arguments in Java

Prior to JDK 5, variable-length arguments could be handled two ways. One using overloaded method(one for each) and another put the arguments into an array, and then pass this array to the method. Both of them are potentially error-prone and require more code. The varargs feature offers a simpler, better option.

Syntax of varargs :
A variable-length argument is specified by three periods(…). For Example:

public static void fun(int ... a) 
{
   // method body
}

This syntax tells the compiler that fun( ) can be called with zero or more arguments. As a result, here a is implicitly declared as an array of type int[].

// Java program to demonstrate varargs 
class Test1 
{ 
    // A method that takes variable number of intger 
    // arguments. 
    static void fun(int ...a) 
    { 
        System.out.println("Number of arguments: " + a.length); 
  
        // using for each loop to display contents of a 
        for (int i: a) 
            System.out.print(i + " "); 
        System.out.println(); 
    } 
  
    // Driver code 
    public static void main(String args[]) 
    { 
        // Calling the varargs method with different number 
        // of parameters 
        fun(100);         // one parameter 
        fun(1, 2, 3, 4);  // four parameters 
        fun();            // no parameter 
    } 
}

}
Output:

Number of arguments: 1
100 
Number of arguments: 4
1 2 3 4 
Number of arguments: 0
 

Explanation of above program :

  • The … syntax tells the compiler that varargs has been used and these arguments should be stored in the array referred to by a.
  • The variable a is operated on as an array. In this case, we have defined the data type of a as int. So it can take only integer values. The number of arguments can be found out using a.length, the way we find the length of an array in Java.

    Note: A method can have variable length parameters with other parameters too, but one should ensure that there exists only one varargs parameter that should be written last in the parameter list of the method declaration.

    int nums(int a, float b, double … c)

Important points:

  • Vararg Methods can also be overloaded but overloading may lead to ambiguity.
  • Prior to JDK 5, variable length arguments could be handled into two ways : One was using overloading, other was using array argument.
  • There can be only one variable argument in a method.
  • Variable argument (varargs) must be the last argument.

Source: https://www.geeksforgeeks.org/variable-arguments-varargs-in-java/

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