如果我从第一个ArrayList中删除了一个值，如何在两个ArrayList上获得相同的位置

Question

I have two ArrayLists

ArrayList<String> firstList = new ArrayList<>(Arrays.asList("king", "king", "queen", "jack", "queen"));

ArrayList<String> secondList = new ArrayList<>(Arrays.asList("one", "one", "one", "two", "one"));

In the List named firstList I'll remove the duplicate using Set<String> hashSet = new HashSet<>(firstList); and the output will be "king", "queen", "jack"

What I want to do is get the position on the secondList equal to the position on the firstList .

The current output is (king & one), (queen, one), (jack, one)

What I want the output to be is (king, one), (queen, one), (jack, two)

If any of you could help me, I would appreciate it a lot.

Answer 1

Assuming your two input lists are always the same length you can do something simple like:

public static void main(String[] args) {
    List<String> firstList  = new ArrayList<>(Arrays.asList("king", "king", "queen", "jack", "queen"));
    List<String> secondList = new ArrayList<>(Arrays.asList("one", "one", "one", "two", "one"));

    List<String> cards = new ArrayList<>();
    List<String> positions = new ArrayList<>();
    for(int i = 0; i< firstList.size(); i++){
        String temp = firstList.get(i);
        if(!cards.contains(temp)){
            cards.add(temp); 
            positions.add(secondList.get(i)); 
        }
    }
    System.out.println(cards);
    System.out.println(positions);
}

Answer 2

Use a Map . In Java 8, it would be (in the form of a passing unit test):

    final List<String> one = asList("king", "king", "queen", "jack", "queen");
    final List<String> two = asList("one", "one", "one", "two", "one");

    //Guards against IndexOutOfBoundsExceptions
    final int size = Math.min(one.size(), two.size()); 
    //LinkedHashMap to preserve key ordering
    final Map<String,String> map = new LinkedHashMap<>(size);
    for(int i = 0; i < size; i++) {
        map.putIfAbsent(one.get(i), two.get(i));
    }

    final String actual = map.entrySet().stream()
            .map(e -> String.format("[%s,%s]", e.getKey(), e.getValue()))
            .collect(Collectors.joining(","));
    final String expected = "[king,one],[queen,one],[jack,two]";
    assertEquals(expected, actual);

For Java 7, you need to check the Map doesn't already contain the key before you add it. putIfAbsent() does this for you otherwise.

You can stream the Map values and keys afterwards if you want to do different things with them:

    final String keys = String.join(",", map.keySet());
    assertEquals("king,queen,jack", keys);

    final String values = String.join(",", map.values());
    assertEquals("one,one,two", values);