java code Explain
\n##### int r = rand.nextInt(total); Generate a random index r within the range [0, total)\n\n##### int x = map.getOrDefault(r, r);     Get the original index a
\n##### int r = rand.nextInt(total); Generate a random index r within the range [0, total)\n\n##### int x = map.getOrDefault(r, r);     Get the original index associated with r from the map. If r is not in the map, it returns r as the default value. This means that if r has not been flipped before, x will be the same as r\n\n##### map.put(r, map.getOrDefault(total, total)); Update the mapping in the map by swapping the values for indices r and total. This is done to ensure that each cell has an equal probability of being selected during the flipping operation\n\n#### why x/col and x%col  => x/col give row , x%col give col number of that element \n\n\n# Code\n\n```\nclass Solution {\n    HashMap<Integer, Integer> map;\n    int row;\n    int col;\n    Random ran;\n    int total;\n\n    public Solution(int m, int n) {\n        map = new HashMap<>();\n        ran = new Random();\n        row = m;\n        col = n;\n        total = row * col;\n    }\n\n    public int[] flip() {\n        int r = ran.nextInt(total);\n        int x = map.getOrDefault(r, r);\n        total--;\n        map.put(r, map.getOrDefault(total, total));\n        \n        return new int[] { x / col, x % col };\n    }\n\n    public void reset() {\n        map.clear();\n        total = row * col;\n    }\n}\n\n/**\n * Your Solution object will be instantiated and called as such:\n * Solution obj = new Solution(m, n);\n * int[] param_1 = obj.flip();\n * obj.reset();\n */\n```
['Java']