java 两个千万级别数据的list去重

测试的机器为4核4线程，16G内存

public static void main(String[] args) {
        long time = System.currentTimeMillis();
        List<String> list = new ArrayList();
        for (int i = 0; i < 1000000; i++) {
            int start=10000000;
            int end=99999999;
            int number = new Random().nextInt(end - start + 1) + start;
            list.add(String.valueOf(number));
        }
        long time1 = System.currentTimeMillis();
        System.out.println("第一次处理耗时："+(time1 - time));
        List<String> list2 = new ArrayList();
        for (int i = 0; i < 10000000; i++) {
            int start=10000000;
            int end=99999999;
            int number = new Random().nextInt(end - start + 1) + start;
            list2.add(String.valueOf(number));
        }
        long time2 = System.currentTimeMillis();
        System.out.println("第二次处理耗时："+(time2 - time1));
        //最后结果集
        List<String> resultList = new ArrayList<>();
        //中间存储
        Map<String, String> map = new HashMap<>();
        list2.forEach(i2 -> {
            map.put(i2 + "", i2);
        });
        list.forEach(i1 -> {
            String m = map.get(i1 + "");
            //如果为空，则证明list2中无该数据
            if (m == null) {
                resultList.add(i1);
            }
        });
        long time3 = System.currentTimeMillis();
        System.out.println("第三次处理耗时："+(time3 - time2));
        System.out.println("差集的数量为："+resultList.size());
    }