java - What's the fastest way to initialize a large list of integers?

Question

I need to pre-populate a List with a large number of integer values.

Is there are faster way to do this other than iteration?

Current Code:

class VlanManager {
    Queue<Integer> queue = Lists.newLinkedList();

    public VlanManager(){
    for (int i = 1; i < 4094; i++) {
        queue.add(i);
    }
}

This code is in the constructor of a class that is created pretty frequently so I'd like this to be as efficient (read:performance not lines of code) as possible

Answer 1

4094 isnt to many items to loop but if it is getting called very frequently you might look at doing something with a static variable.

private static Integer[] theList;

static {
    theList = new Integer[4094];
    for (int i = 1; i < 4094; i++) {
        theList[i-1] = i;
    }
}

then make that list a List

Queue<Integer> intQue = new LinkedList(Arrays.asList(theList));

---

There is a danger of using this method if you have a list of mutable objects. Heres an example of what can happen. Integers are immutable so this doesnt actually apply to your question as it stands

class MyMutableObject {
    public int theValue;
}

class Test {

    private static MyMutableObject[] theList;

    static {
        theList = new MyMutableObject[4094];
        for (int i = 1; i <= 4094; i++) {
            theList[i-1] = new MyMutableObject();
            theList[i-1].theValue = i;
        }
    }

    public static void main(String [] args) {
        Queue<MyMutableObject> que = new LinkedList(Arrays.asList(theList));
        System.out.println(que.peek().theValue); // 1
        // your actually modifing the same object as the one in your static list
        que.peek().theValue = -100; 
        Queue<MyMutableObject> que2 = new LinkedList(Arrays.asList(theList));
        System.out.println(que2.peek().theValue); // -100
    }
}

---

@Bohemian Has some good points on using a static List instead of an array, while the performance gains are very small they are none the less performance gains. Also because the 'array' is actually only ever being used as a List not an array it should be declared as such.

private static List<Integer> theList;

static {
    theList = new ArrayList(4094);
    for (Integer i = 0; i < 4094; i++) {
        theList.add(i+1);
    }
}