Java varargs

Definition

This code declare a function that can take arbitrary number of parameters. The parameters must be the same type int.

void sampleFunction(int... args) {
    System.out.print(args.length);
    
    for (int i = 0; i < args.length; i++) {
        System.out.print(args[i]);
    }
}

It’s possible to mix varargs with other parameter types, like this:

void sampleMixingFunction(String name, Date date, int... args) {
    ...
}

The varargs must be the last parameters in function signature.
It’s not allowed to declare multiple varargs in one function.

Usage

With any number of parameters

You can pass any number of parameters to function, but must be the same type.

void test() {
    sampleFunction(1);         // will print: 11
    sampleFunction(1,2);       // will print: 212
    sampleFunction(1,2,3,4,5); // will print: 512345
}

With none parameter

You can also pass none parameter too. In this case, the array length is zero.

void test() {
    sampleFunction(); // will print: 0
}

Note: In some case, it may lead to misusing when user accidentally calls function with none parameter. To prevent it, we don’t allow empty parameters calling by making first parameter mandatory:

void sampleFunction(int mandatoryArg, int... args) {
    ...
}

By this, calling to sampleFunction with none parameter will result compile time error.

With single null parameter

If you pass null, the array will be null. Thus, access to args.length will result NullPointerException.

void test() {
    sampleFunction(null); // will throw NullPointerException
}