What are the rules to be followed while using varargs in java?

Since JSE1.5 you can pass a variable number of values as argument to a method. These arguments are known as var args and they are represented by three dots (…)

Syntax

public myMethod(int ... a) {
   // method body
}

Rules to follow while using varargs in Java

• We can have only one variable argument per method. If you try to use more than one variable arguments a compile time error is generated.

Example

In the following Java example we are trying to accepts two varargs from the method sample().

public class VarargsExample{
   void demoMethod(int... ages), String... names) {
      for (int arg: ages) {
         System.out.println(arg);
      }
   }
}

Compile time error

On compiling, the above program generates the following error(s) −

VarargsExample.java:2: error: ')' expected
   void demoMethod(int... ages, String... names) {
                              ^
VarargsExample.java:2: error: <identifier> expected
   void demoMethod(int... ages, String... names) {
                                       ^
VarargsExample.java:2: error: <identifier> expected
   void demoMethod(int... ages, String... names) {
                                               ^
3 errors

• In the list of arguments of a method varargs must be the last one. Else a compile time error will be generated.

Example

In the following example, the VarargsExample class has a method with name demoMethod() which accepts 3 arguments: a vararg, a String and an integer.

Here we are making the varargs the 1st in the arguments list.

public class VarargsExample{
   void demoMethod(int... marks, String name, int age) {
      System.out.println();
      System.out.println("Name: "+name);
      System.out.println("Age: "+age);
      System.out.print("Marks: ");
      for (int m: marks) {
         System.out.print(m+" ");
      }
   }
}

Compile time error

On compiling, the above program generates the following error.

VarargsExample.java:2: error: ')' expected
   void demoMethod(int... marks, String name, int age) {
                            ^
VarargsExample.java:2: error: <identifier> expected
   void demoMethod(int... marks, String name, int age) {
                                            ^
VarargsExample.java:2: error: <identifier> expected
   void demoMethod(int... marks, String name, int age) {
                                                     ^
3 errors

If you compile the same in eclipse it generates an (same) error suggesting that the variable argument should be the last in the list as shown below −

If you want to make this program work you need to place the variable argument at the end of the arguments list of the method.

public class VarargsExample{
   void demoMethod(String name, int age, int... marks) {
      System.out.println();
      System.out.println("Name: "+name);
      System.out.println("Age: "+age);
      System.out.print("Marks: ");
      for (int m: marks) {
         System.out.print(m+" ");
      }
   }
   public static void main(String args[] ){
      VarargsExample obj = new VarargsExample();
      obj.demoMethod("Krishna", 23, 90, 95, 80, 69 );
      obj.demoMethod("Vishnu", 22, 91, 75, 94 );
      obj.demoMethod("Kasyap", 25, 85, 82);
      obj.demoMethod("Vani", 25, 93);
   }
}

Output

Name: Krishna
Age: 23
Marks: 90 95 80 69
Name: Vishnu
Age: 22
Marks: 91 75 94
Name: Kasyap
Age: 25
Marks: 85 82
Name: Vani
Age: 25
Marks: 93