Collection add elements in single line

Passing arrays instance arguments in single line of code is very useful. For example you can do something like this:

addNumbers(new int[] {1,2,3});

And it will work perfectly, but for collections you can't to that. However using anonymous inner classes with instance initialization we can get similar effect:

addNumbers(new ArrayList<Integer>(3) {{ add(1); add(2); add(3); }});

If we expand this code, it will be more clear how it works.

addNumbers(new ArrayList<Integer>(3) {//anonymous class
  //instance initialization block
  { 
    add(1); 
    add(2); 
    add(3); 
  }
});

Just for completeness here are addNumber methods:

private static int addNumbers(int[] numbers) {
    int result = 0;
    for (int number : numbers) {
        result += number;
    }
    return result;
}

private static Integer addNumbers(Collection<Integer> numbers) {
    Integer result = 0;
    for (Integer number : numbers) {
        result += number;
    }
    return result;
}