VarArgs in java

• The full form of var-arg is variable length arguments.
• Till JDK 1.4 we must define overloaded methods to pass different list of arguments .
• But using this feature we can define method to pass ZERO to 'n'  number of arguments.
• Syntax: After data type we must place three dots.

1.          void method(int... i){
2.          }

• Internally Var-arg is a single dimensional array. So we can also pass single dimensional array as argument.

1. package instanceofjavaforus;
2. public class VDemo{ 
3.  void print(int... args){
4. for(int i=0;i<args.length;i++){
5. System.out.println(args[i]);
6. }
7. System.out.println();
8. }
9. public static void main(String args[]){
10.  Vdemo obj= new Vdemo();
11. int x={1,2};
12. obj.print(x);// works fine
13. obj.print(1,2,3,4);// works fine
14. obj.print();// works fine
15. //int... var=new int[5]; compile time error: not a valid statement
16. } 
17.  
18. Output:
19. 1
20. 2
21. 
    
22. 1
23. 2
24. 3
25. 4

It must be last argument:

1. package instanceofjavaforus;
2. public class VDemo{ 
3. void print(int x){
4.  System.out.println("int x");
5. }
6.  
7. void print(int x, int y){
8.  System.out.println("int x, int y");
9. } 
10.  void print(int x, int y,int... args){
11. System.out.println("int x, int y,int... args");
12. }
13. void print(int... args){
14. System.out.println("int x, int y");
15. }
16.  public static void main(String args[]){
17.  Vdemo obj= new Vdemo();
18. int x={1,2};
19. obj.print(1);
20. obj.print(x);// works fine
21. obj.print(1,2,3,4);// works fine
22. obj.print();// works fine
23. //int... var=new int[5]; compile time error: not a valid statement
24. } 
25. 
    
26. Output:
27. int x
28. int x, int y
29. int x, int y,int... args
    

• if we declared  placed any type after var-arg in the arguments list of a method then it throws a compile time error.

1. void print(int x, int y, int...args, int z){// compile time error
2. // throws Compile time error:The variable argument type int of the method print must be the
3.  // last parameter
4.  System.out.println("int x, int y");
5. } 
6.  void print(int x, int y,int... args){  // valid
7. System.out.println("int x, int y,int... args");
8. }

Overloading method with normal and varargs types :

1. package instanceofjavaforus;
2. public class VDemo{ 
3.  void print(int... args){
4. System.out.println("var arg method");
5. }
6. void print(int args){
7. System.out.println("normal method");
8. }
9.  
10. public static void main(String args[]){
11.  Vdemo obj= new Vdemo();
12. obj.print(1);// works fine
13. } 
14.  }
15. Output:
16. normal method

Overloading method with normal and varargs types in super and sub classes:

var args Program 1:

1. package instanceofjavaforus;
2. public class VDemo{ 
3.  void print(int... args){
4. System.out.println("super class method");
5. }
6. } 

1. package instanceofjavaforus;
2. public class Test extends VDemo{ 
3.  void print(int args){
4. System.out.println("sub class method");
5. }
6. public static void main(String args[]){
7.  VDemo vobj= new VDemo();
8. vobj.print(10);
9. Test tobj= new Test();
10. tobj.print(10);
11. }
12. }
13. OutPut:
14. Super class method
15. Sub class method

var args Program 2:

1. package instanceofjavaforus;
2. public class VDemo{ 
3.  void print(int args){
4. System.out.println("super class method");
5. }
6. }

1. package instanceofjavaforus;
2.  
3. public class Test extends VDemo{ 
4.  
5.  void print(int... args){
6. System.out.println("sub class method");
7. }
8. public static void main(String args[]){
9.  
10.  VDemo vobj= new VDemo();
11. vobj.print(10);
12. Test tobj= new Test();
13. tobj.print(10);
14.  
15. }
16. }
17. OutPut:
18. Super class method
19. Super class method