java求几个hashmap中key的并集，输出value

思路是挨个挨个Map遍历,将结果放入一个汇总的map,希望有更漂亮的方案

public class MapMerge {
    public static void main(String[] args) {
        List<HashMap<String,Integer>> list = generate();
        HashMap<String,String> result = new HashMap<>();
        HashMap<String,Integer> tmpmap = new HashMap<>();
        //循环遍历每个Map,合并成一个大的map
        for (int i = 0; i < list.size(); i++) {
            //遍历Map中的每一个元素
            tmpmap = list.get(i);
            if(tmpmap==null||tmpmap.size()<1){
                continue;
            }
            Iterator<String> it = tmpmap.keySet().iterator();
            while(it.hasNext()){
                String key = it.next();
                Integer value = tmpmap.get(key);
                //如果在结果中已经存在key,
                if(result.containsKey(key)){
                    //该键已经统计过了
                }else{
                    //前i个hashmap里面没有值,把剩下的hashmap的值挨个取出.
                    StringBuilder sb = new StringBuilder();
                    for (int j = 0; j < i; j++) {
                        sb.append(";-1");
                    }

                    for (int j = i; j < list.size(); j++) {
                        sb.append(";"+getValue(list.get(j),key));
                    }
                    sb.deleteCharAt(0);
                    result.put(key, sb.toString());
                }
            }
        }
        System.out.println("map合并以后:\n" + result);      
    }

    private static int getValue(HashMap<String,Integer> map,String key){
        Integer result = map.get(key);
        return result==null?-1:result;
    }

    //随机构造n个hashmap
    public static List<HashMap<String,Integer>> generate(){
        List<HashMap<String,Integer>> list = new ArrayList<>();
        Random r = new Random();
        int i=(int) (Math.round(Math.random()*3 + 3));//hashMap的数量
        System.out.println("输入hashMap的数量:   "+i);

        int tmpSize = 0;
        HashMap tmpmap = null;
        for (int j = 0; j < i; j++) {
            tmpmap = new HashMap<String,Integer>();
            //hashMap的长度
            tmpSize = (int) (Math.round(Math.random()*10 + 4));
            for (int k = 0; k < tmpSize; k++) {
                //随机键值对
                String key = String.valueOf((char)(int) (Math.round(Math.random()*25 + 97)));
                int value = (int) (Math.round(Math.random()*8 + 1));
                tmpmap.put(key, value);
            }
            list.add(tmpmap);
            System.out.println(tmpmap);
        }
        return list;
    }
}