Difference between ArrayList and LinkedList in Java - whys for performance

I thought I understand the difference between ArrayList and LinkedList theoretically pretty well. However, for the first time, I put it on a small test, and the tests came out, which is very different from my expectations.

Expectations:

• Arraylist will be slower than LinkedList when pasting on since it has to “shift” elements for a linked list, just updating 2 links.

  Reality: at most iterations it was the same. For a few select iterations, this was slower.

• The Arrailist will be slower than the LinkedList when deleting at the beginning, since it has to “shift” the elements, for Linkedlist, it just negates one element.

  Reality: performance was the same when moving away from beg.

Test case: 1,000,000 items

public static void main(String[] args) {
    int n = 1000000;

    List arrayList = new ArrayList(n+10);
    long milis = System.currentTimeMillis();
    for(int i= 0 ;i<n;i++){
        arrayList.add(i);
    }
    System.out.println("insert arraylist takes "+(System.currentTimeMillis()-milis)+" ms");

    List linkedList = new LinkedList();
    milis = System.currentTimeMillis();
    for(int i= 0 ;i<n;i++){
        linkedList.add(i);
    }
    System.out.println("insert linkedlist takes "+(System.currentTimeMillis()-milis)+" ms");

    //System.out.println("Adding at end");
    milis = System.currentTimeMillis();
    arrayList.add(n-5,n+1);
    System.out.println("APPEND arraylist takes "+(System.currentTimeMillis()-milis)+" ms");

    milis = System.currentTimeMillis();
    linkedList.add(n-5,n+1);
    System.out.println("APPEND linkedlist takes "+(System.currentTimeMillis()-milis)+" ms");

    //add at front
    milis = System.currentTimeMillis();
    arrayList.add(0,0);
    System.out.println("INSERT BEG arraylist takes "+(System.currentTimeMillis()-milis)+" ms");

    milis = System.currentTimeMillis();
    linkedList.add(0,0);
    System.out.println("INSERT BEG linkedlist takes "+(System.currentTimeMillis()-milis)+" ms");

    //add at middle
    milis = System.currentTimeMillis();
    arrayList.add(n/2,n/2);
    System.out.println("INSERT MIDDLE arraylist takes "+(System.currentTimeMillis()-milis)+" ms");

    milis = System.currentTimeMillis();
    linkedList.add(n/2,n/2);
    System.out.println("INSERT MIDDLE linkedlist takes "+(System.currentTimeMillis()-milis)+" ms");

    //get from front, mid, end
    milis = System.currentTimeMillis();
    arrayList.get(0);
    System.out.println("get front arraylist takes "+(System.currentTimeMillis()-milis)+" ms");

    milis = System.currentTimeMillis();
    linkedList.get(0);
    System.out.println("get front linkedlist takes "+(System.currentTimeMillis()-milis)+" ms");

    milis = System.currentTimeMillis();
    arrayList.get(n/2);
    System.out.println("get MIDDLE arraylist takes "+(System.currentTimeMillis()-milis)+" ms");

    milis = System.currentTimeMillis();
    linkedList.get(n/2);
    System.out.println("get MIDDLE linkedlist takes "+(System.currentTimeMillis()-milis)+" ms");

    milis = System.currentTimeMillis();
    arrayList.get(n-4);
    System.out.println("get last arraylist takes "+(System.currentTimeMillis()-milis)+" ms");

    milis = System.currentTimeMillis();
    linkedList.get(n-4);
    System.out.println("get last linkedlist takes "+(System.currentTimeMillis()-milis)+" ms");

    //delete from front, mid, end.
    milis = System.currentTimeMillis();
    arrayList.remove(0);
    System.out.println("del front arraylist takes "+(System.currentTimeMillis()-milis)+" ms");

    milis = System.currentTimeMillis();
    linkedList.remove(0);
    System.out.println("del front linkedlist takes "+(System.currentTimeMillis()-milis)+" ms");

    milis = System.currentTimeMillis();
    arrayList.remove(n/2);
    System.out.println("del mid arraylist takes "+(System.currentTimeMillis()-milis)+" ms");

    milis = System.currentTimeMillis();
    linkedList.remove(n/2);
    System.out.println("del mid linkedlist takes "+(System.currentTimeMillis()-milis)+" ms");

    milis = System.currentTimeMillis();
    arrayList.remove(n-4);
    System.out.println("del end arraylist takes "+(System.currentTimeMillis()-milis)+" ms");

    milis = System.currentTimeMillis();
    linkedList.remove(n-4);
    System.out.println("del end linkedlist takes "+(System.currentTimeMillis()-milis)+" ms");

}

Output log

insert arraylist takes 141 ms
insert linkedlist takes 312 ms
APPEND arraylist takes 0 ms
APPEND linkedlist takes 0 ms
INSERT BEG arraylist takes 0 ms
INSERT BEG linkedlist takes 0 ms
INSERT MIDDLE arraylist takes 0 ms
INSERT MIDDLE linkedlist takes 0 ms
get front arraylist takes 0 ms
get front linkedlist takes 0 ms
get MIDDLE arraylist takes 0 ms
get MIDDLE linkedlist takes 16 ms
get last arraylist takes 0 ms
get last linkedlist takes 0 ms
del front arraylist takes 0 ms
del front linkedlist takes 0 ms
del mid arraylist takes 0 ms
del mid linkedlist takes 15 ms
del end arraylist takes 0 ms
del end linkedlist takes 0 ms

And what is the reason? Used by JDK 1.6.

EDIT: after using System.nanotime (), it gave me the answers as I expected. Agreed, this is the only test and should be averaged.

insert arraylist takes 137076082 ns
insert linkdlist takes 318985917 ns
APPEND arraylist takes 69751 ns
APPEND linkdlist takes 98126 ns
**INSERT BEG arraylist takes 2027764 ns
INSERT BEG linkdlist takes 53522 ns**
INSERT MIDDLE arraylist takes 1008253 ns
INSERT MIDDLE linkdlist takes 10395846 ns
get front arraylist takes 42364 ns
get front linkdlist takes 77473 ns
get MIDDLE arraylist takes 39499 ns
get MIDDLE linkdlist takes 9645996 ns
get last arraylist takes 46165 ns
get last linkdlist takes 43446 ns
**del front arraylist takes 1720329 ns
del front linkdlist takes 108063 ns**
del mid arraylist takes 1157398 ns
del mid linkdlist takes 11845077 ns
del end arraylist takes 54149 ns
del end linkdlist takes 49744 ns