two equal array lists but java does not see equal

Question

Here I declare two array lists

ArrayList<Location> possibleMoves = new ArrayList<Location>();
possibleMoves.add(new Location(0, 1));
possibleMoves.add(new Location(1, 0));

ArrayList<Location> possibleMoves1 = new ArrayList<Location>();
possibleMoves1.add(new Location(0, 1));
possibleMoves1.add(new Location(1, 0));

its obvious that those 2 array lists are the same, but when I run this check it always seems to fail.

if(possibleMoves == possibleMoves1){
  System.out.println("lol");
}

I have also tried this and it failed

assertTrue("Player 1 1st piece could play to the left and down!",
arrayListsEqual(possibleMoves, possibleMoves1));

this is the method of arrayListsEqual

private boolean arrayListsEqual(ArrayList<Location> a, ArrayList<Location> b) {
    if (a.size() != b.size()) {
        return false;
    }
    int size = a.size();
    boolean thisOneFound = false;
    for (int i = 0; i < size; i++) {
        thisOneFound = false;
        for (int j = 0; j < size; j++) {
            if (a.get(i).equals(b.get(j))) {
                thisOneFound = true;
                break;
            }
        }
        if (!thisOneFound) {
            return false;
        }
    }
    return true;
}

@Duncan its given in a test file that is made by the professor of the course — user3567826, Apr 24 '14 at 08:24
@user3567826 Please show us the definition of `arrayListsEqual`. — Duncan Jones, Apr 24 '14 at 08:25
@user3567826 Interesting - that equality method doesn't care about the order of items in the list. How strange. — Duncan Jones, Apr 24 '14 at 08:30
@Duncan i have no idea how it is not working, this is getting quite frustrating :d — user3567826, Apr 24 '14 at 08:32
`Location` needs an `equals` method since you are using multiple instances of Location for the same position. — greg-449, Apr 24 '14 at 08:51

score 4 · Answer 1 · answered Apr 24 '14 at 08:12

4

2 issues:

The "Location" objects are different instances. so they are totally unrelated objects.
The list themselves are different instances.

first: you need to check equality with the "equals" method of the lists:

 list1.equals(list2).

also, you need to make sure you save the SAME object in those lists (by using the same instance) or to implement the "equals" and "hashmap" methods in the "Location" class.

once that is done it should work.

good luck :)

answered Apr 24 '14 at 08:12

APT

365
2
11

i understand this but unfortunately i can't modify this assertTrue("Player 1 1st piece could play to the left and down!", arrayListsEqual(possibleMoves, possibleMoves1)); its given in the test file that was created by the professor, so supposedly i should make this work with the assertListsEqual – user3567826 Apr 24 '14 at 08:19
2

@user3567826 In that case your only requirement is to implement `equals()` and `hashCode` in your `Location` class. – Duncan Jones Apr 24 '14 at 08:31
@Duncan you are right!! its stupid of me to miss this! thanks, i guess when you stay awake for 2 days working you miss the small stuff :D – user3567826 Apr 24 '14 at 08:41

score 0 · Answer 2 · edited May 23 '17 at 12:06

0

Please read about the difference between == and equals. == checks whether both References refer to the same instance whereas equals tests for equality. Have a look at the answers to this question.

edited May 23 '17 at 12:06

Community

1
1

answered Apr 24 '14 at 08:10

Axel

13,939
5
50
79

score 0 · Answer 3 · answered Apr 24 '14 at 08:12

0

You cannot compare reference objects with == , ArrayList is not a primitive data type.

answered Apr 24 '14 at 08:12

Immy

57
2
10

two equal array lists but java does not see equal

3 Answers3