Java根據權重按比例返回相應的值

根據權重等比例返回相應的值，有很多種實現方式和途徑。這裏簡單演示兩種Java的程序實現，先貼代碼：

 public static void main(String[] args) throws ParseException {
        Map<String, Integer> map = new HashMap<>();
        map.put("A", 20);
        map.put("B", 10);
        map.put("C", 40);
        map.put("D", 30);

        //獲取權重總和
        Integer sum = map.values().parallelStream().reduce(Integer::sum).get();
        //測試500W次
        Integer total = 5000000;

        //第一種方式
        int a = 0, b = 0, c = 0, d = 0;
        for (int i = 0; i < total; i++) {
            Integer random = new Random().nextInt(sum);
            for (String str : map.keySet()) {
                int weight = map.get(str);
                if (random > weight) {
                    random -= weight;
                } else {
                    switch (str) {
                        case "A":
                            a++;
                            break;
                        case "B":
                            b++;
                            break;
                        case "C":
                            c++;
                            break;
                        case "D":
                            d++;
                            break;
                    }
                    break;
                }
            }
        }
        System.out.println("第一種方式：");
        System.out.println("A:" + a + "  佔比：" + ((float) a / total));
        System.out.println("B:" + b + "  佔比：" + ((float) b / total));
        System.out.println("C:" + c + "  佔比：" + ((float) c / total));
        System.out.println("D:" + d + "  佔比：" + ((float) d / total));

        //第二種方式
        List<String> list = new ArrayList<>();
        map.keySet().forEach(key -> {
            int value = map.get(key);
            for (int i = 0; i < value; i++) {
                list.add(key);
            }
        });
        Collections.shuffle(list);
        int A = 0, B = 0, C = 0, D = 0;
        for (int i = 0; i < total; i++) {
            String str = list.get(new Random().nextInt(sum));
            switch (str) {
                case "A":
                    A++;
                    break;
                case "B":
                    B++;
                    break;
                case "C":
                    C++;
                    break;
                case "D":
                    D++;
                    break;
            }
        }
        System.out.println("\n第二種方式：");
        System.out.println("A:" + A + "  佔比：" + ((float) A / total));
        System.out.println("B:" + B + "  佔比：" + ((float) B / total));
        System.out.println("C:" + C + "  佔比：" + ((float) C / total));
        System.out.println("D:" + D + "  佔比：" + ((float) D / total));
    }

實驗結果：

根據結果可以看出，兩種方式都能滿足要求。但相對而言，第一種方式更能省內存。