CODEWITHSUNDEEP
java
user6792790
user6792790

Reputation: 688

Using Map in Java. How to not overwrite Value?

    for(int i = 0; i < Board.NUM_OF_ROWS; i++) {
        for(int j = 0; j < Board.NUM_OF_COLS; j++) {
            if(piece.canMove(board, piece.getX(), piece.getY(), i, j)) {
                mappedPosition.put(i, j);
            }
        }
    }

In this code, I am trying to add a pair of (x,y) coordinate of a movable Position of a chess "piece".

For example, I was expecting it to add [2,2], [2,4], [3,1], [3,5], [5,1], [5,5], [6,2], [6,4]

But when I use put, it overwrites the Value when it has the same Key. So [2,2] just becomes [2,4] eventually.

How can I get the full list of the pair without overwriting it?

Upvotes: 0

Views: 2592

Answers (5)

Ori Marko
Ori Marko

Reputation: 58812

You can use Apache MultiMap for holding several values per key

MultiMap mhm = new MultiValueMap();
mhm.put(key, "A"); mhm.put(key, "B");
mhm.put(key, "C");
Collection coll = (Collection) mhm.get(key);

coll will be a collection containing "A", "B", "C".

Upvotes: 0

f1l2
f1l2

Reputation: 491

In that case you can also use a Multimap. The API is similar, but the value is always a Collection.

http://google.github.io/guava/releases/23.0/api/docs/com/google/common/collect/Multimap.html

Upvotes: 0

pradeep
pradeep

Reputation: 295

You can, use Guava's Multimap.

Multimap<Integer, String> multimap = ArrayListMultimap.create();
multimap.put(1, "rohit");
multimap.put(1, "jain");

System.out.println(multimap.get(1));  // Prints - [rohit, jain]

Upvotes: 0

Nikolas
Nikolas

Reputation: 44456

Map uses the unique key identifiers thus it's impossible to have the same key twice and more.

Create the class holding the two coordinate values you need.

public class BoardPoint {

    private int x;
    private int y;

    public BoardPoint(int x, int y) {
        this.x = x;
        this.y = y;
    }

    // getters & setters
}

The class above will be useful in case you need to scale: implement more variables or perform some operations over the pair of values. If you need just a POJO (plain-old Java object) the class java.awt.Point should be enough as @XtremeBaumer said id the comments.

Upvotes: 3

Roee Gavirel
Roee Gavirel

Reputation: 19453

Map by definition is key --> value. And each key can only have one value at each moment. You can either use set when the values are pair of (x,y) or just a list, it depends on how you wish to use this information later.

Upvotes: 0

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