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Swapping objects between two arraylists

Naveen Ramanathan

Joined: Apr 20, 2009
Posts: 8

I was wondering if there is a way to swap objects between two arraylists? I have two ArrayLists of Players with a skill number (random number between 1-10) and am having a hard time figuring out how to swap the Player with the minimum skill from either team(team1/team2) with the Player with the maximum skill from either team (team1/team2).

The logic is as below:

SkillDifferenceCompare skillDifferenceCompare = new SkillDifferenceCompare();

swapListMin.add(Collections.min(team1, skillDifferenceCompare));
swapListMax.add(Collections.max(team1, skillDifferenceCompare));

swapListMin.add(Collections.min(team2, skillDifferenceCompare));
swapListMax.add(Collections.max(team2, skillDifferenceCompare));

swapListMin.remove(Collections.max(swapListMin, skillDifferenceCompare));
swapListMax.remove(Collections.min(swapListMax, skillDifferenceCompare));

System.out.println("Before Swapping: ");

What I am doing is finding the Player with the min skill in either team1/team2 using a comparator(on skilldifference instance variable of type Integer of Player), storing them in a swapListMin arraylist then finding the Player with the max skill in either team1/team2 using the same comparator and storing them in swapListMin.
At the point, swapListMin has 2 Players with min skills from team1 and team 2. swapListMax has 2 Players with max skills from team1 and team2. Then I remove the min skill Player from swapListMax and max skill Player from swapListMin. This leaves me with just 1 element in swapListMin (who is basically the Player with the lowest skill in either of the teams put together) and the opposite in swapListMax.

What i want to do now is to swap these players in swapListMin and swapListMax and put them back in their opposite teams (swap them basically). I was able to swap the Players from swapListMin and swapListMax using a tempList. But I am not able to figure out how to put them back in the team arraylist (team1 or team2).

tempSwapList = swapListMin;
swapListMin = swapListMax;
swapListMax = tempSwapList;

The Player object has attributes: playerTeam (either 1 or 2), playerSorted( false by default, to be set to true once swapping is done), skillDifference(random number between 1 to 10).

I would really appreciate it if someone could guide me on how to go about performing the swap.

Thanks in advance !

Ankit Garg

Joined: Aug 03, 2008
Posts: 9453

Hi Naveen, welcome to javaranch.

Well I couldn't understand the complete logic that you are trying to explain here, but swaping objects in ArrayList should not be a tough task. ArrayList is ordered and also provides index based access to elements. So it should be as simple as this

[Edit: added welcome message]

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Naveen Ramanathan

Joined: Apr 20, 2009
Posts: 8
Naveen Ramanathan

Joined: Apr 20, 2009
Posts: 8
Thanks Ankit.. I got it to work finally...
My apologies for the long delay in reply..

I agree. Here's the link:
subject: Swapping objects between two arraylists
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