How to check if an object exists in a LinkedList in java?

user_811433 0
Viewed 2227

A LinkedList contains a set of Integer[]. Each Integer[] in the list has 2 numbers. Ex of the linked list: 

Integer[]{1,2}, Integer[]{2,3}.....

Before adding another Integer[] to this LinkedList, I wanto check if another Integer[] with the same data already exists.

Ex: Object to add = Integer[] {2,3}. But this already exists in the LinkedList.

So I want to avoid adding this.

How to verify that object already exists? Is there an inbuild function that can be used? contains() didnt do the trick.

linked-list contains java
4 Answers

I think you better use a specific class if you are treating coordinates, as an Integer[] is useless for only two numbers, and will cause some problems with contains() and other List methods like .sort() as well.

You better create a Coordinate class, which will hold the two values:

public class Coordinate{
    private int x;
    private int y;

    //getters and setters, constructor
    @Override
    public boolean equals(Object o) {
        if (o == this) return true;
        if (!(o instanceof Coord)) {
            return false;
        }
        Coordinate coord = (Coordinate) o;
        return coord.x == x &&
                coord.y == y;
    }

    @Override
    public int hashCode() {
        int result = 17;
        result = 31 * result + x;
        result = 31 * result + y;
        return result;
    }
}

Then you can use:

LinkedList<Coordinate>

Note:

Note that using a Set implementation will be better here, it will prevent having duplicates in the set of coordinates, so we don't need to check for it manually.

user_36696240

Well, you can do it the dumb way:

boolean exists = false;
for (Integer[] integers : list) {  // list being the LinkedList
    if (Arrays.equals(integers, value)) {
        exists = true;
        break;
    }
}
if (!exists) {
    list.add(value);
}
user_17716340

You can use Stream with Set to solve your problem like below:

 List<Set<Integer>> list = new LinkedList<>();
    list.add(Stream.of(1, 2).collect(Collectors.toSet()));

    Set<Integer> s1 = new HashSet<>();
    s1.add(1);
    s1.add(2);

    System.out.println(list.contains(s1));

    Set<Integer> s2 = new HashSet<>();
    s2.add(1);
    s2.add(4);
    System.out.println(list.contains(s2));

O/P:

true

false

N.B: You can use ArrayList because yo preserve the sequence as well.

user_71763820

If you really really want to do that with contains() (or have no other choice by whatever reason), you can implement it like that:

    final Integer[] newPair = {2, 3};
    final boolean exists = values.contains(new Object()
    {
        // note that List.contains() javadoc explicitly specifies that 
        // newPair is used as the receiver not the argument for equals()
        @Override
        public final boolean equals(final Object listElement)
        {
            final Integer[] otherPair = (Integer[]) listElement;
            return Arrays.equals(newPair, otherPair);
        }
    });
user_16542330
Related