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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 errorsIf 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
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