Java Method Varargs Overloading

Introduction

We can overload a method with a variable-length argument.

For example, the following program overloads myTest() three times: 

// Varargs and overloading. 
public class Main { 
 
  static void myTest(int ... v) { 
    System.out.print("myTest(int ...): " + 
                     "Number of args: " + v.length + 
                     " Contents: "); 
 
    for(int x : v) {
      System.out.print(x + " "); 
    }/*from   w  w  w.j  a  v  a2  s  .c o m*/
    
 
    System.out.println(); 
  } 
 
  static void myTest(boolean ... v) { 
    System.out.print("myTest(boolean ...) " + 
                     "Number of args: " + v.length + 
                     " Contents: "); 
 
    for(boolean x : v) {
      System.out.print(x + " "); 
    }
    System.out.println(); 
  } 
 
  static void myTest(String msg, int ... v) { 
    System.out.print("myTest(String, int ...): " + 
                     msg + v.length + 
                     " Contents: "); 
 
    for(int x : v) {
      System.out.print(x + " "); 
    }
    System.out.println(); 
  } 
 
  public static void main(String args[])  
  { 
    myTest(1, 2, 3);  
    myTest("Testing: ", 10, 20); 
    myTest(true, false, false); 
  } 
}

We can overload a varargs method in two ways:

  • the types of its vararg parameter can differ.
  • add one or more normal parameters.

A varargs method can be overloaded by a non-varargs method.

Java will invoke the method with single parameter first. 



public class Main
{
   // calculate average
   public static double average(double... numbers)
   {/*from   ww  w. j  a  v  a 2 s  .  c  om*/
      double total = 0.0; 

      // calculate total using the enhanced for statement
      for (double d : numbers)
         total += d;

      return total / numbers.length;
   } 

   public static void main(String[] args) 
   {
      double d1 = 10.0;
      double d2 = 20.0;
      double d3 = 30.0;
      double d4 = 40.0;

      System.out.printf("d1 = %.1f%nd2 = %.1f%nd3 = %.1f%nd4 = %.1f%n%n",
         d1, d2, d3, d4);

      System.out.printf("Average of d1 and d2 is %.1f%n", 
         average(d1, d2)); 
      System.out.printf("Average of d1, d2 and d3 is %.1f%n", 
         average(d1, d2, d3));
      System.out.printf("Average of d1, d2, d3 and d4 is %.1f%n", 
         average(d1, d2, d3, d4));
   } 
}



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