Java HashMap放入for循环中

Question

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);
    }
}

Answer 1

Arrays in Java don't provide an implementation of equals method. Eg, 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.

Answer 2

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.