CODEWITHSUNDEEP
javafor-loophashmap
Lauge
Lauge

Reputation: 33

Java HashMap put in a for loop in

I have a for loop, where i check if there is a certain key in a HashMap, if the key is not there, it should put a new association in the HashMap. The problem is that that it puts the association, but by the next iteration of the loop the association is gone! I don't get it!

public void DrawBoard(ArrayList<Integer[]> BoardList, int FrameX, int FrameY){
    StdDraw.setCanvasSize(FrameX*50, FrameY*50);
    StdDraw.clear(new Color(0,0,0));
    StdDraw.setXscale(0, FrameX);
    StdDraw.setYscale(FrameY, 0);
    Map<Integer[], Color> Coloring = new HashMap<Integer[], Color>();
    for(int i = 0; i < BoardList.size(); i++){
        Integer[] Rectangle = BoardList.get(i);
        Random rand = new Random();
        Integer[] ColorCheck = {Rectangle[2], Rectangle[3]};
        if(Coloring.containsKey(ColorCheck)){
            StdDraw.setPenColor(Coloring.get(ColorCheck));}
        else{ 
        Color newColor = new Color(rand.nextInt(256), rand.nextInt(256), rand.nextInt(256));
        Coloring.put(ColorCheck, newColor);
        StdDraw.setPenColor(newColor);
        }
        double x1 = Rectangle[0];
        double y1 = Rectangle[1];
        double x2 = Rectangle[2];
        double y2 = Rectangle[3];
        StdDraw.filledRectangle(x1+(x2/2), y1+(y2/2), x2/2, y2/2);
    }
}

Upvotes: 0

Views: 1091

Answers (2)

extraneon
extraneon

Reputation: 23950

As Nikita said, arrays don't implement an value-by-value equals. It's just an object equals.

If you want to use this implementation you should use a Map with a custom comparator (like a TreeMap) and use for instance Arrays.equals in the implementation of that comparator. That way the elememts of colorCheck are also checked (array content), and not so much the array reference.

Upvotes: 2

Nikita Rybak
Nikita Rybak

Reputation: 68006

Arrays in Java don't provide an implementation of equals method. E.g., array1.equals(array2) will always be false, even if both arrays contain equal number of the same objects. Therefore, you can't use them as map keys: map.containsKey won't work.

Try lists instead: Arrays.asList(1, 2). Or create a special 'pair' object, since you only hold two elements in array.

Upvotes: 2

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