Java Varargs explained with code samples

Java supports passing a variable number of arguments (varargs) to a method. In this article, I will be explaining this feature.

What is varargs

JDK 5 added the varargs feature, which allow creating a method that accepts a variable number of arguments. Prior to the varargs support, if you wanted to create a method with variable arguments, you either had to overload the method or use a Collection or array as a parameter.

Varargs Syntax

A variable number of arguments is specified using an argument name and three dots. The following code demonstrates this:

void method myMethod(String ...str){//method body}

This specifies a String argument str which is a vararg. So you can invoke this method as follows:

myMethod("a");  //with 1 parametermyMethod("a","b"); //with 2 parametersmyMethod("a", "b", "c"); //with 3 parameters

Code Sample

The following code demonstrates a code sample that uses varargs:

public class VarargDemo {  public static int calculate(int... num) {    int sum = 0;    for (int i : num) {      sum += i;    }    return sum;  }  public static void main(String[] args) {    System.out.println("With one argument:" + calculate(5));    System.out.println("With two arguments:" + calculate(3, 7));    System.out.println("With three arguments:" + calculate(2, 4, 8));  }}

 

This code has a method calculate that accepts a parameter num which is a vararg. It simple returns the num of the values specified in the vararg. It uses a for-each loop to iterate through the vararg. The main method then invokes this method with one, two and three arguments. So this code prints the following output:

With one argument:5With two arguments:10With three arguments:14

Varargs Rules

There are some rules that need to be followed while creating a vararg argument. These are as follows:

  • The vararg must be the last argument in the method declaration. So if a method accepts multiple arguments, the vararg must be the last argument
  • A method cannot have more than one vararg

Conclusion

So in this article, we saw what Java varargs are, how varargs work and how they help in creating methods that accept a variable number of arguments in Java.

 

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